# NASASpaceFlight.com Forum

## Robotic Spacecraft (Astronomy, Planetary, Earth, Solar/Heliophysics) => Space Science Coverage => Topic started by: Star One on 01/22/2017 07:27 PM

Post by: Star One on 01/22/2017 07:27 PM
Seemed a good idea to have a separate thread for miscellaneous exoplanet discoveries.

Is there a circumbinary planet around NSVS 14256825?

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The cyclic behaviour of (O-C) residuals of eclipse timings in the sdB+M eclipsing binary NSVS 14256825 was previously attributed to one or two Jovian-type circumbinary planets. We report 83 new eclipse timings that not only fill in the gaps in those already published but also extend the time span of the (O-C) diagram by three years. Based on the archival and our new data spanning over more than 17 years we re-examined the up to date system (O-C). The data revealed systematic, quasi-sinusoidal variation deviating from an older linear ephemeris by about 100 s. It also exhibits a maximum in the (O-C) near JD 2,456,400 that was previously unknown. We consider two most credible explanations of the (O-C) variability: the light propagation time due to the presence of an invisible companion in a distant circumbinary orbit, and magnetic cycles reshaping one of the binary components, known as the Applegate or Lanza-Rodono effect. We found that the latter mechanism is unlikely due to the insufficient energy budget of the M-dwarf secondary. In the framework of the third-body hypothesis, we obtained meaningful constraints on the Keplerian parameters of a putative companion and its mass. Our best-fitting model indicates that the observed quasi-periodic (O-C) variability can be explained by the presence of a brown dwarf with the minimal mass of 15 Jupiter masses rather than a planet, orbiting the binary in a moderately elliptical orbit (~ 0.175) with the period of ~ 10 years. Our analysis rules out two planets model proposed earlier.

https://arxiv.org/abs/1701.05211
Post by: Star One on 01/26/2017 06:54 PM
Wolf 1061 unlikely to host habitable worlds.

http://www.centauri-dreams.org/?p=37016

Here's the pre-print.

Characterization of the Wolf 1061 Planetary System

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A critical component of exoplanetary studies is an exhaustive characterization of the host star, from which the planetary properties are frequently derived. Of particular value are the radius, temperature, and luminosity, which are key stellar parameters for studies of transit and habitability science. Here we present the results of new observations of Wolf~1061, known to host three super-Earths. Our observations from the Center for High Angular Resolution Astronomy (CHARA) interferometric array provide a direct stellar radius measurement of 0.3207±0.0088~R⊙, from which we calculate the effective temperature and luminosity using spectral energy distribution models. We obtained seven years of precise, automated photometry that reveals the correct stellar rotation period of 89.3±1.8~days, finds no evidence of photometric transits, and confirms the radial velocity signals are not due to stellar activity. Finally, our stellar properties are used to calculate the extent of the Habitable Zone for the Wolf~1061 system, for which the optimistic boundaries are 0.09--0.23~AU. Our simulations of the planetary orbital dynamics shows that the eccentricity of the Habitable Zone planet oscillates to values as high as ∼0.15 as it exchanges angular momentum with the other planets in the system.

https://arxiv.org/abs/1612.0934
Post by: ikke666 on 01/27/2017 04:59 PM
is there a list of stars that have planets on web?  ::) prefably with the kind of planet (gas giant, earth like,...)
Post by: testguy on 01/27/2017 05:29 PM

http://exoplanet.eu/catalog/
Post by: hop on 01/28/2017 06:00 AM
There's also the NASA Exoplanet archive http://exoplanetarchive.ipac.caltech.edu/
Post by: Star One on 01/28/2017 12:13 PM
Took the Keck observatory seven years of observations to produce this.

A Four Planet System in Orbit, Directly Imaged and Remarkable

http://www.manyworlds.space/index.php/2017/01/24/a-four-planet-system-in-orbit-directly-imaged-and-remarkable/
Post by: ikke666 on 01/28/2017 03:55 PM
thanks for the sites  ;D
Post by: Star One on 02/02/2017 08:38 PM
Water spotted in the atmosphere of nearby hot Jupiter exoplanet

https://www.newscientist.com/article/mg23331111-800-water-spotted-in-the-atmosphere-of-nearby-hot-jupiter-exoplanet/
Post by: Star One on 02/13/2017 07:36 PM
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Washington, DC— An international team of astronomers released the largest-ever compilation of exoplanet-detecting observations made using a technique called the radial velocity method. They demonstrated how these observations can be used to hunt for planets by detecting more than 100 potential exoplanets, including one orbiting the fourth-closest star to our own Solar System, which is about 8.1 light years away from Earth. The paper is published in The Astronomical Journal.
The radial velocity method is one of the most successful techniques for finding and confirming planets. It takes advantage of the fact that in addition to a planet being influenced by the gravity of the star it orbits, the planet’s gravity also affects the star. Astronomers are able to use sophisticated tools to detect the tiny wobble the planet induces as its gravity tugs on the star.
The virtual mountain of data released to the public in this paper was gathered as part of a two-decade radial velocity planet-hunting program that uses a spectrometer called HIRES, mounted on the 10-meter Keck-I telescope of the W.M. Keck Observatory atop Mauna Kea in Hawaii. The compilation includes almost 61,000 individual measurements made of more than 1,600 stars. By making the data public, the team is offering unprecedented access to one of the best exoplanet searches in the world.
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One of these probable planets is around a star called GJ 411, also known as Lalande 21185. It is the fourth-closest star to our own Sun and is only about 40 percent the mass of the Sun. The planet has a very short orbital period of just under 10 days, so it is no Earth-twin. However, the inferred planet, GJ 411b, continues a trend that has been seen in the overall population of detected exoplanets: the smallest planets are found around the smallest stars.

https://carnegiescience.edu/news/team-makes-planet-hunting-group-effort-finds-more-100-candidates#
Post by: Star One on 02/15/2017 07:11 PM
Planet-Induced Stellar Pulsations in HAT-P-2's Eccentric System

J. de Wit, N.K. Lewis, H.A. Knutson, J. Fuller, V. Antoci, B.J. Fulton, G. Laughlin, D. Deming, A. Shporer, K. Batygin, N.B. Cowan, E. Agol, A.S. Burrows, J.J. Fortney, J. Langton, A.P. Showman
(Submitted on 13 Feb 2017)

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Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet's atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet-star interactions in HAT-P-2's eccentric planetary system gained from the analysis of 350 hr of 4.5 micron observations with the Spitzer Space Telescope. The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary companion, HAT-P-2 b. The extensive coverage allows us to better differentiate instrumental systematics from the transient heating of HAT-P-2 b's 4.5 micron photosphere and yields the detection of stellar pulsations with an amplitude of approximately 40 ppm. These pulsation modes correspond to exact harmonics of the planet's orbital frequency, indicative of a tidal origin. Transient tidal effects can excite pulsation modes in the envelope of a star, but, to date, such pulsations had only been detected in highly eccentric stellar binaries. Current stellar models are unable to reproduce HAT-P-2's pulsations, suggesting that our understanding of the interactions at play in this system is incomplete.

https://arxiv.org/abs/1702.03797

We need your help on a brand new astronomy project – Backyard Worlds: Planet 9
In this project you’ll be searching through images from NASA’s Wide-field Infrared Survey Explorer (WISE) mission, hunting for objects such as brown dwarfs and low-mass stars in our Solar System’s neighbourhood. You may find an object closer than Proxima Centauri (the closest star to the Sun) or even discover the Sun’s hypothesized ninth planet, which models suggest might appear in these images!
Start hunting right now at www.backyardworlds.org.
Post by: Mongo62 on 02/28/2017 07:23 PM
Towards Detection of Exoplanetary Rings Via Transit Photometry: Methodology and a Possible Candidate (https://arxiv.org/abs/1702.08252)

Abstract: Detection of a planetary ring of exoplanets remains as one of the most attractive but challenging goals in the field. We present a methodology of a systematic search for exoplanetary rings via transit photometry of long-period planets. The methodology relies on a precise integration scheme we develop to compute a transit light curve of a ringed planet. We apply the methodology to 89 long-period planet candidates from the Kepler data so as to estimate, and/or set upper limits on, the parameters of possible rings. While a majority of our samples do not have a sufficiently good signal-to-noise ratio for meaningful constraints on ring parameters, we find that six systems with a higher signal-to-noise ratio are inconsistent with the presence of a ring larger than 1.5 times the planetary radius assuming a grazing orbit and a tilted ring. Furthermore, we identify five preliminary candidate systems whose light curves exhibit ring-like features. After removing four false positives due to the contamination from nearby stars, we identify KIC 10403228 as a reasonable candidate for a ringed planet. A systematic parameter fit of its light curve with a ringed planet model indicates two possible solutions corresponding to a Saturn-like planet with a tilted ring. There also remain other two possible scenarios accounting for the data; a circumstellar disk and a hierarchical triple. Due to large uncertain factors, we cannot choose one specific model among the three.
Post by: Star One on 03/10/2017 06:51 PM
Another close by system that may turn out to be suitable for exo-atmosphere observations.

HD 219134: A Nearby System with Multiple Transits

http://www.centauri-dreams.org/?p=37300

Here's the paper.

http://www.nature.com/articles/s41550-017-0056#references
Post by: jebbo on 03/13/2017 05:24 PM
In news other than Trappist-1, this on Kepler-444 is interesting:

https://arxiv.org/abs/1703.03417 (https://arxiv.org/abs/1703.03417)

The masses imply a density around that of water, which is quite remarkable as the planets have been at >600K for about 11 billion years ... so keeping hold of volatiles is quite a feat. Oh, it also implies an origin beyond the ice line

--- Tony
Post by: Bynaus on 03/13/2017 05:36 PM
Only the nominal densities are close to water, the uncertainties are quite high. Within only one standard deviation (68% confidence interval), the densities are between 0.5 g/cm3 and 3.5 g/cm3 (see Table 2), so a rocky composition can certainly not be excluded at this point. Like you say, it would be very surprising if such low-mass planets would have kept their volatiles at 600 K over the 11 Ga age of the system.
Post by: jebbo on 03/13/2017 05:42 PM
Absolutely ... and I'm wary of numbers from Bayesian methods (e.g. see Kass & Rafferty, 1995)

Shame the predicted RV is too low, though I wonder if at magnitude 9, we might get transmission spectroscopy

Edit: added figure from arxiv.org paper
--- Tony
Post by: Star One on 03/13/2017 08:10 PM
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The search for extraterrestrial life is increasingly informed by our knowledge of exoplanets. Within three decades, we may know whether extrasolar life is rare.

Post by: Star One on 03/14/2017 11:10 AM
Mysterious celestial object could be an elusive brown dwarf or a free-floating planet

The object is not part of the AB Doradus moving group, as previous hypothesised.

http://www.ibtimes.co.uk/mysterious-celestial-object-could-be-elusive-brown-dwarf-free-floating-planet-1611441

More details on this topic in this article including the relevant paper.

https://phys.org/news/2017-03-mysterious-isolated-astronomers.html
Post by: Star One on 03/15/2017 08:11 PM
Not an exoplanet but an interesting star instead.

Isotope shift and search for metastable superheavy elements in astrophysical

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Spectral lines belonging to the short-lifetime heavy radioactive elements up to Es (Z=99) have been found in the spectra of the Przybylski's star. We suggest that these unstable elements may be decay products of a "magic" metastable nucleus belonging to the the island of stability where the nuclei have a magic number of neutrons N=184. The laboratory-produced nuclei have a significantly smaller number of neutrons. To identify spectra of the N=184 isotopes of these nuclei and their neutron-reach superheavy decay products in astrophysical data we calculate the isotope shift which should be added to the laboratory - measured wavelenghs. The results for the isotopic shifts in the strongest optical electromagnetic transitions in No, Lr, Nh, Fl,and Z=120 elements are presented.

https://arxiv.org/abs/1703.04250
Post by: Bynaus on 03/17/2017 06:20 AM
Plenty of Earth-mass worlds around nearby red dwarfs (one of them in the HZ, 3.8 pc away).

https://arxiv.org/abs/1703.05386

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The HARPS search for southern extra-solar planets XLI. A dozen planets around the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628, and GJ 3293

Context. Low mass stars are currently the best targets for searches for rocky planets in the habitable zone of their host star. Over the last 13 years, precise radial velocities measured with the HARPS spectrograph have identified over a dozen super-Earths and Earth-mass planets (msin i<10Mearth ) around M dwarfs, with a well understood selection function. This well defined sample informs on their frequency of occurrence and on the distribution of their orbital parameters, and therefore already constrains our understanding of planetary formation. The subset of these low-mass planets that were found within the habitable zone of their host star also provide prized targets for future atmospheric biomarkers searches. Aims. We are working to extend this planetary sample to lower masses and longer periods through dense and long-term monitoring of the radial velocity of a small M dwarf sample. Methods. We obtained large numbers of HARPS spectra for the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628 and GJ 3293, from which we derived radial velocities (RVs) and spectroscopic activity indicators. We searched them for variabilities, periodicities, Keplerian modulations and correlations, and attribute the radial-velocity variations to combinations of planetary companions and stellar activity. Results. We detect 12 planets, of which 9 are new with masses ranging from 1.17 to 10.5 Mearth . Those planets have relatively short orbital periods (P<40 d), except two of them with periods of 217.6 and 257.8 days. Among these systems, GJ 273 harbor two planets with masses close to the one of the Earth. With a distance of 3.8 parsec only, GJ 273 is the second nearest known planetary system - after Proxima Centauri - with a planet orbiting the circumstellar habitable zone.

I know we already know this from Kepler, but its really astonishing how these red dwarf star systems are all choke full with massive terrestrial-to-neptunian worlds.

GJ 273 - also known as Luyten's Star - is currently located only 1.2 LY away from Procyon. It has a ca. 3 Earth-mass planet which recieves 1.06 times the solar insolation on Earth.
Post by: Star One on 03/28/2017 08:17 PM
Jason Wright investigates Przybylski’s Star.

http://sites.psu.edu/astrowright/2017/03/15/przybylskis-star-i-whats-that/
Post by: CuddlyRocket on 03/31/2017 11:55 AM
Eric Mamajek‏
@EricMamajek

Fig. 7 will make #exoplanet jaws drop https://arxiv.org/abs/1703.10375 "Fulton Gap" clearly separates super-Earths & sub-Neptunes #Kepler #Keck #NASA

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We find evidence for a bimodal distribution of small planet sizes. Sub-Neptunes and super-Earths appear to be two distinct planet classes. Planets tend to prefer radii of either ∼1.3 R⊕ or ∼2.4 R⊕, with relatively few planets having radii of 1.5–2.0 R⊕.
Post by: Star One on 04/04/2017 08:35 PM
Venus 2.0 Discovered In Our Own Backyard

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And now, a team of international astronomers has announced the discovery of an extra-solar body that is similar to another terrestrial planet in our own Solar System. It’s known as Kepler-1649b, a planet that appears to be similar in size and density to Earth and is located in a star system just 219 light-years away. But in terms of its atmosphere, this planet appears to be decidedly more “Venus-like” (i.e. insanely hot!)

The team’s study, titled “Kepler-1649b: An Exo-Venus in the Solar Neighborhood“, was recently published in The Astronomical Journal. Led by Isabel Angelo – of the SETI Institute, NASA Ames Research Center, and UC Berkley – the team included researchers also from SETI and Ames, as well as the NASA Exoplanet Science Institute (NExScl), the Exoplanet Research Institute (iREx), the Center for Astrophysics Research, and other research institutions.

https://www.universetoday.com/134849/venus-2-0-discovered-back-yard/
Post by: Star One on 04/06/2017 08:26 PM
Atmosphere around super-Earth detected

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Astronomers have detected an atmosphere around the super-Earth GJ 1132b. This marks the first detection of an atmosphere around a low-mass super-Earth, in terms of radius and mass the most Earth-like planet around which an atmosphere has yet been detected. Thus, this is a significant step on the path towards the detection of life on an exoplanet. The team, which includes researchers from the Max Planck Institute for Astronomy, used the 2.2-m ESO/MPG telescope in Chile to take images of the planet's host star, GJ 1132, and measured the slight decrease in brightness as the planet and its atmosphere absorbed some of the starlight while passing directly in front of their host star.

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The team used the GROND imager at the 2.2-m ESO/MPG telescope of the European Southern Observatory in Chile to observe the planet simultaneously in seven different wavelength bands. GJ 1132b is a transiting planet: From the perspective of an observer on Earth, it passes directly in front of its star every 1.6 days, blocking some of the star's light.

The size of stars like GJ 1132 is well known from stellar models. From the fraction of starlight blocked by the planet, astronomers can deduce the planet's size—in this case around 1.4 times the size of the Earth. Crucially, the new observations showed the planet to be larger at one of the infrared wavelengths than at the others. This suggests the presence of an atmosphere that is opaque to this specific infrared light (making the planet appear larger) but transparent at all the others. Different possible versions of the atmosphere were then simulated by team members at the University of Cambridge and the Max Planck Institute for Astronomy. According to those models, an atmosphere rich in water and methane would explain the observations very well.

The discovery comes with the usual exoplanet caveats: while somewhat larger than Earth, and with 1.6 times Earth's mass (as determined by earlier measurements), observations to date do not provide sufficient data to decide how similar or dissimilar GJ 1132b is to Earth. Possibilities include a "water world" with an atmosphere of hot steam.

The presence of the atmosphere is a reason for cautious optimism. M dwarfs are the most common types of star, and show high levels of activity; for some set-ups, this activity (in the shape of flares and particle streams) can be expected to blow away nearby planets' atmospheres. GJ 1132b provides a hopeful counterexample of an atmosphere that has endured for billion of years (that is, long enough for us to detect it). Given the great number of M dwarf stars, such atmospheres could mean that the preconditions for life are quite common in the universe.

In any case, the new observations make GJ 1132b a high-priority target for further study by instruments such as the Hubble Space Telescope, ESO's Very Large Telescope, and the James Webb Space Telescope slated for launch in 2018.

https://m.phys.org/news/2017-04-atmosphere-super-earth.html

Stargazing Live viewers find four-planet solar system via crowd-sourcing project

http://mobile.abc.net.au/news/2017-04-06/stargazing-live-four-planets-discovered-in-new-solar-system/8423142
Post by: CuddlyRocket on 04/06/2017 10:20 PM
Stargazing Live viewers find four-planet solar system via crowd-sourcing project

http://mobile.abc.net.au/news/2017-04-06/stargazing-live-four-planets-discovered-in-new-solar-system/8423142

Interesting 3:2 orbital resonances between planets b and c, c and d, and d and e.
Post by: jebbo on 04/07/2017 08:50 AM
Interesting 3:2 orbital resonances between planets b and c, c and d, and d and e.

A very interesting compact system around a late G dwarf, which makes these planets *hot*.  Sadly, no observed TTVs so it will be a while before we know mass/density.

Worth noting this was from the Campaign 12 raw cadence data (the processed data has not yet been released to MAST).  I'm hoping this sets a precedent for future campaigns :-)

This weekend, I'll try and produce a light curve for this one (but my raw cadence code still needs a fair bit of debug).

There are quite a few new candidates from this Exoplanet Explorers search, some in earlier quarters, so once again, the human eyeball has found things missed by the automated pipelines.  Clearly some will be false positives (BGEB contamination is most likely).

Edit: taking much longer than expected as the MAST download of the raw cadence data is glacial.

--- Tony
Post by: CuddlyRocket on 04/17/2017 08:01 AM
Cross-posting from the 'NASA's Trappist-1 Announcement - Feb 22, 2017' thread.

Updated Masses for the TRAPPIST-1 Planets (arXiv) (https://arxiv.org/abs/1704.04290)

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The newly detected TRAPPIST-1 system, with seven low-mass, roughly Earth-sized planets transiting a nearby ultra-cool dwarf, is one of the most important exoplanet discoveries to date. The short baseline of the available discovery observations, however, means that the planetary masses (obtained through measurement of transit timing variations of the planets of the system) are not yet well constrained. The masses reported in the discovery paper were derived using a combination of photometric timing measurements obtained from the ground and from the Spitzer spacecraft, and have uncertainties ranging from 30\% to nearly 100\%, with the mass of the outermost, P=18.8d, planet h remaining unmeasured. Here, we present an analysis that supplements the timing measurements of the discovery paper with 73.6 days of photometry obtained by the K2 Mission. Our analysis refines the orbital parameters for all of the planets in the system. We substantially improve the upper bounds on eccentricity for inner six planets (finding e<0.02 for inner six known members of the system), and we derive masses of 0.79±0.27M⊕, 1.63±0.63M⊕, 0.33±0.15M⊕, 0.24+0.56−0.24M⊕, 0.36±0.12M⊕, 0.566±0.038M⊕, and 0.086±0.084M⊕ for planets b, c, d, e, f, g, and h, respectively.

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Figure 4 indicates that – to within the errors of our determinations – the four most distant planets are consistent with pure water compositions, and in any event, are substantially less dense either Mars or Venus.
Post by: Bynaus on 04/18/2017 06:52 AM
Cross-posting from the 'NASA's Trappist-1 Announcement - Feb 22, 2017' thread.

Updated Masses for the TRAPPIST-1 Planets (arXiv) (https://arxiv.org/abs/1704.04290)

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The newly detected TRAPPIST-1 system, with seven low-mass, roughly Earth-sized planets transiting a nearby ultra-cool dwarf, is one of the most important exoplanet discoveries to date. The short baseline of the available discovery observations, however, means that the planetary masses (obtained through measurement of transit timing variations of the planets of the system) are not yet well constrained. The masses reported in the discovery paper were derived using a combination of photometric timing measurements obtained from the ground and from the Spitzer spacecraft, and have uncertainties ranging from 30\% to nearly 100\%, with the mass of the outermost, P=18.8d, planet h remaining unmeasured. Here, we present an analysis that supplements the timing measurements of the discovery paper with 73.6 days of photometry obtained by the K2 Mission. Our analysis refines the orbital parameters for all of the planets in the system. We substantially improve the upper bounds on eccentricity for inner six planets (finding e<0.02 for inner six known members of the system), and we derive masses of 0.79±0.27M⊕, 1.63±0.63M⊕, 0.33±0.15M⊕, 0.24+0.56−0.24M⊕, 0.36±0.12M⊕, 0.566±0.038M⊕, and 0.086±0.084M⊕ for planets b, c, d, e, f, g, and h, respectively.

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Figure 4 indicates that – to within the errors of our determinations – the four most distant planets are consistent with pure water compositions, and in any event, are substantially less dense either Mars or Venus.

Very interesting, the densities of the planets are now (in g/cm3):

b: 3.4 +- 1.2
c: 7.63 +- 3.02
d: 3.95 +- 1.86
e: <5.71
f: 1.74 +- 0.61
g: 2.18 +- 0.28
h: <2.54

It is quite remarkable that the density drops significantly below the 3-5 range (= Earth-like, rocky planets) for the planets with equilibrium temperatures below 0°C, the freezing point of water (at 1 bar, but its quite possible that these planets have ~1 bar atmospheres). This might suggest the outer planets f,g,h are essentially super-Ganymedes.
Post by: Star One on 04/19/2017 08:54 PM
Newly Discovered Exoplanet May be Best Candidate in Search for Signs of Life

Transiting rocky super-Earth found in habitable zone of quiet red dwarf star

An exoplanet orbiting a red dwarf star 40 light-years from Earth may be the new holder of the title “best place to look for signs of life beyond the Solar System”. Using ESO’s HARPS instrument at La Silla, and other telescopes around the world, an international team of astronomers discovered a “super-Earth” orbiting in the habitable zone around the faint star LHS 1140. This world is a little larger and much more massive than the Earth and has likely retained most of its atmosphere. This, along with the fact that it passes in front of its parent star as it orbits, makes it one of the most exciting future targets for atmospheric studies. The results will appear in the 20 April 2017 issue of the journal Nature.

The newly discovered super-Earth LHS 1140b orbits in the habitable zone around a faint red dwarf star, named LHS 1140, in the constellation of Cetus (The Sea Monster) [1]. Red dwarfs are much smaller and cooler than the Sun and, although LHS 1140b is ten times closer to its star than the Earth is to the Sun, it only receives about half as much sunlight from its star as the Earth and lies in the middle of the habitable zone. The orbit is seen almost edge-on from Earth and as the exoplanet passes in front of the star once per orbit it blocks a little of its light every 25 days.

“This is the most exciting exoplanet I’ve seen in the past decade,” said lead author Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (Cambridge, USA). “We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”

"The present conditions of the red dwarf are particularly favourable — LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars," explains team member Nicola Astudillo-Defru from Geneva Observatory, Switzerland [2].

For life as we know it to exist, a planet must have liquid surface water and retain an atmosphere. When red dwarf stars are young, they are known to emit radiation that can be damaging for the atmospheres of the planets that orbit them. In this case, the planet's large size means that a magma ocean could have existed on its surface for millions of years. This seething ocean of lava could feed steam into the atmosphere long after the star has calmed to its current, steady glow, replenishing the planet with water.

The discovery was initially made with the MEarth facility, which detected the first telltale, characteristic dips in light as the exoplanet passed in front of the star. ESO’s HARPS instrument, the High Accuracy Radial velocity Planet Searcher, then made crucial follow-up observations which confirmed the presence of the super-Earth. HARPS also helped pin down the orbital period and allowed the exoplanet’s mass and density to be deduced [3].

The astronomers estimate the age of the planet to be at least five billion years. They also deduced that it has a diameter 1.4 times larger than the Earth — almost 18 000 kilometres. But with a mass around seven times greater than the Earth, and hence a much higher density, it implies that the exoplanet is probably made of rock with a dense iron core.

This super-Earth may be the best candidate yet for future observations to study and characterise its atmosphere, if one exists. Two of the European members of the team, Xavier Delfosse and Xavier Bonfils both at the CNRS and IPAG in Grenoble, France, conclude: “The LHS 1140 system might prove to be an even more important target for the future characterisation of planets in the habitable zone than Proxima b or TRAPPIST-1. This has been a remarkable year for exoplanet discoveries!” [4,5].

In particular, observations coming up soon with the NASA/ESA Hubble Space Telescope will be able to assess exactly how much high-energy radiation is showered upon LHS 1140b, so that its capacity to support life can be further constrained.

Further into the future — when new telescopes like ESO’s Extremely Large Telescope are operating — it is likely that we will be able to make detailed observations of the atmospheres of exoplanets, and LHS 1140b is an exceptional candidate for such studies.

http://www.eso.org/public/news/eso1712/?lang
Post by: Star One on 04/20/2017 08:58 PM
This is an excellent article on LHS 1140b including future plans for its study.

Newfound Super-Earth Boosts Search for Alien Life

Planet LHS 1140 b orbits a dim red dwarf star just 40 light-years away, making it a prime target for life-finding telescopes

https://www.scientificamerican.com/article/newfound-super-earth-boosts-search-for-alien-life/
Post by: Star One on 04/26/2017 06:52 PM
Speculations on Habitable Zone Waterworlds

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What to make of Fergus Simpson’s new paper on waterworlds, suggesting that most habitable zone planets are of this type? If such worlds are common, we may find that most planets in the habitable zones of their stars are capable of evolving life, but unlikely to host technological civilizations. An explanation for the so-called ‘Fermi Paradox’? Possibly, but there are all kinds of things that could account for our inability to see other civilizations, most of them covered by Stephen Webb in his If the Universe Is Teeming with Aliens … Where Is Everybody? (2nd ed., Springer 2015), which offers 75 solutions to the problem.

Simpson (University of Barcelona) makes his case in the pages of Monthly Notices of the Royal Astronomical Society, arguing that the balance maintained by a planetary surface with large amounts of both land and water is delicate. The author’s Bayesian statistical analysis suggests that most planets are dominated either by water or land, most likely water. Earth may, then, be something of an outlier, with most planets over 90 percent covered in water.

http://www.centauri-dreams.org/?p=37561
Post by: CuddlyRocket on 04/27/2017 01:53 AM
There seems to be a confusion in terminology prevalent. Is a waterworld a world covered in water, but which, like the Earth, is predominately made of rock and metal; or is a waterworld one which is predominately made of water (ice, actually)?

I think of a waterworld as being the latter, with the former described as an oceanworld. But I could be under a misapprehension! :)
Post by: Star One on 04/27/2017 08:47 AM
There seems to be a confusion in terminology prevalent. Is a waterworld a world covered in water, but which, like the Earth, is predominately made of rock and metal; or is a waterworld one which is predominately made of water (ice, actually)?

I think of a waterworld as being the latter, with the former described as an oceanworld. But I could be under a misapprehension! :)

I think of it as a watery Earth myself as that seemed to be what the article was referencing.
Post by: Star One on 04/27/2017 08:56 PM
Seems a decent summary.

New Planet Discoveries Signal a Shift in the Hunt for Alien Life

http://news.nationalgeographic.com/2017/04/new-planets-life-close-earth-space-science/
Post by: Star One on 04/28/2017 07:10 PM
Planetary Discovery around Ultracool Star

Quote
Small planets may be common around ultracool dwarfs, an idea that previous microlensing discoveries reinforce, along with the work on protoplanetary disks and the seven planets orbiting TRAPPIST-1. As to our expectations regarding planets in the galactic bulge as opposed to the disk, the jury is still out. The planets Spitzer has thus far found in its microlensing campaign for the galactic distribution of planets are all located in the disk. We have two upcoming Spitzer microlensing campaigns, one this year and one next, which should offer additional insights. The key question: Is the galactic bulge deficient in planets?

http://www.centauri-dreams.org/?p=37573

Here is the paper.

https://arxiv.org/abs/1703.08548
Post by: Star One on 05/03/2017 04:50 PM
Astronomers confirm nearby star a good model of our early solar system

http://www.news.iastate.edu/news/2017/05/02/eridani

http://www.centauri-dreams.org/?p=37606
Post by: Star One on 05/10/2017 08:46 PM
Exploring the Planet / Brown Dwarf Boundary

http://www.centauri-dreams.org/?p=37665
Post by: missinglink on 05/10/2017 09:10 PM
Poll:

If & when a future ultra-sensitive spectroscope detects chlorophyll in an exoplanet's atmosphere -- meaning ongoing photosynthesis by abundant plant life -- will NASA (plus maybe other government's space agencies) mount a hugely expensive effort (hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears? Knowing that radio transmission of results won't be received by anyone currently living? And with no guarantee of success?

Yes: Explore & investigate is in our genes, must find out if this is a Second Earth that can be our lifeboat & refuge

No: We will never leave solar system, age of discovery is over
Post by: gospacex on 05/10/2017 09:33 PM
Is it a trick question?

"(hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears" - well, such a probe could reach its destination somewhere in the year 50000, at best. Does not make sense, if you ask me...
Post by: Star One on 05/11/2017 06:20 AM
Is it a trick question?

"(hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears" - well, such a probe could reach its destination somewhere in the year 50000, at best. Does not make sense, if you ask me...
Answer invent a quicker way to get there obviously.
Post by: Torbjorn Larsson, OM on 05/11/2017 11:08 AM
Poll:

If & when a future ultra-sensitive spectroscope detects chlorophyll in an exoplanet's atmosphere -- meaning ongoing photosynthesis by abundant plant life -- will NASA (plus maybe other government's space agencies) mount a hugely expensive effort (hundreds of billions of dollars) to send a robotic probe to that planet over a distance of, say, 20 lightyears? Knowing that radio transmission of results won't be received by anyone currently living? And with no guarantee of success?

Yes: Explore & investigate is in our genes, must find out if this is a Second Earth that can be our lifeboat & refuge

No: We will never leave solar system, age of discovery is over

I'll echo that: Is it a trick question?

Some of the problems:
- Science & technology & societal development is not decided by polls.
- Finding biotic signatures is discovery. The (non)question is how fast this age of discovery will put up larger observatories to find out more. My guess: very quickly.

The lifeboat/refuge/faster probes perspective is Utopia fantasy, as far as I can see. [Admittedly: 1. I am tired of seeing such ideas around discussions containing a smidgen of science. The at odds juxtaposition is like scratching sounds from a window. But never mind that. 2. Something like Starshot may be feasible and complement other methods of discovery. Scaled up such can carry spores or even seeds, but not implant anything like our biosphere - such evolution will end up somewhere else in phylogenetic tree space. It would be a possible life refugia at best. But life is likely common, seeing how fast it emerged on Earth.]

Relativity physics puts a hard limit on economical expansion or 'refuge' (if not refugia) ideas. Whether or not individuals or even worlds would - like any parent - put aside resources for direct colonization is an open question.

[But I am reminded of the xkcd comic where Randall shows that on an exponential scale - the scale of economical growth - colonizing the Oort cloud is the largest effort after the Moon. From the Oort cloud the distance to the next cloud is nothing in relation. So if and when we colonize the resource full innards of Oort objects and put rocket engines on the outside - because orbiting is such a bounded life - I expect we will seed the galaxy. My guess: it will happen. But I do not see any connection with fears of extinction.]

Here is the crucial point as far as I can see: our species will go extinct. Nothing can or should stop that anymore than we can or should stop the death of individuals, assuming we want to continue evolving in order for the process of life to continue. The average lifetime of a mammal species is 1-2 Myrs, and we can see from H. erectus that the Homo lineage is, despite the bushy behavior, no exception. Even colonization won't stop that since speciation is an incipient process as soon as population interbreeding drops under an average of 1 breeding/generation. [A somewhat curious result from population genetics, the population sizes are divided out of the problem.]

Life on the other hand may never go extinct as long as it finds a habitable environment. Our one sample is roughly as old as the habitable environment on Earth, indicating a mature biosphere is hardy. I expect our soon-to-come - give or take a Myr - descendants will remember us fondly in the way we remember our great grandparents. "But they lived then, we live now."
Post by: missinglink on 05/11/2017 08:34 PM
Not a "trick question", just wanted to get an idea how NSF Forum members expect that the relevant organizations -- and the public, which funds them -- will react to detection of life on exoplanets.

Post by: dror on 05/11/2017 09:14 PM
My whole interest in space derives from the hope to see that picture.
Sadly, I don't think the reaction will be as immediate or effective as you have suggested. I do hope, though, that it will encourage more reasonable discussions, put some sense in some people who needs it, and allow for a general increase in funding for research.
We must remember, though, that while an exoplanet may save the human race, it will not save the humans on this planet, and won't save this planet from them.
Post by: Star One on 05/11/2017 09:19 PM
NASA Study Finds Unexpectedly Primitive Atmosphere Around ‘Warm Neptune’

Quote
A study combining observations from NASA’s Hubble and Spitzer space telescopes reveals that the distant planet HAT-P-26b has a primitive atmosphere composed almost entirely of hydrogen and helium. Located about 437 light years away, HAT-P-26b orbits a star roughly twice as old as the sun.

The analysis is one of the most detailed studies to date of a “warm Neptune,” or a planet that is Neptune-sized and close to its star. The researchers determined that HAT-P-26b’s atmosphere is relatively clear of clouds and has a strong water signature, although the planet is not a water world. This is the best measurement of water to date on an exoplanet of this size.

The discovery of an atmosphere with this composition on this exoplanet has implications for how scientists think about the birth and development of planetary systems. Compared to Neptune and Uranus, the planets in our solar system with about the same mass, HAT-P-26b likely formed either closer to its host star or later in the development of its planetary system, or both.

https://www.nasa.gov/feature/goddard/2017/nasa-study-finds-unexpectedly-primitive-atmosphere-around-warm-neptune
Post by: missinglink on 05/12/2017 02:54 PM
We must remember, though, that while an exoplanet may save the human race, it will not save the humans on this planet, and won't save this planet from them.
True, true...

Life on exoplanets may be detected sooner than we think, if this proposal comes to fruition: https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Solar_Gravity_Lens_Mission/

Just imagine, an habitable planet that doesn't need to be terraformed ... because it's already teeming with lush plant life. Send seed ships with human eggs and sperm, make of it a Second Earth. Ethical to do this to another biosphere? I guess not. Anyway, cost is prohibitive and First Earth gets no return on investment after bankrupting itself to stage the mission. So, probably never happen.
Post by: gospacex on 05/12/2017 05:50 PM
We must remember, though, that while an exoplanet may save the human race, it will not save the humans on this planet, and won't save this planet from them.
True, true...

Life on exoplanets may be detected sooner than we think, if this proposal comes to fruition: https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Solar_Gravity_Lens_Mission/

Travel to 550 AU to be able to observe a single target? Because steering this telescope would be... difficult, to say the least.

Quote
Just imagine, an habitable planet that doesn't need to be terraformed ... because it's already teeming with lush plant life. Send seed ships with human eggs and sperm, make of it a Second Earth. Ethical to do this to another biosphere? I guess not.

How about founding "bacteria have rights!" movement? It's sickening to think what massacres some people perpetrate daily, using only toothbrushes!
Post by: Oli on 05/14/2017 03:42 PM
We must remember, though, that while an exoplanet may save the human race, it will not save the humans on this planet, and won't save this planet from them.
True, true...

Life on exoplanets may be detected sooner than we think, if this proposal comes to fruition: https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Solar_Gravity_Lens_Mission/

Travel to 550 AU to be able to observe a single target? Because steering this telescope would be... difficult, to say the least.

If we find a planet with the right atmosphere (i.e. Earth-like), such a mission could certainly be worth it. I'm not aware of any other method that could deliver a 1000x1000px image of an exoplanet other than truly gigantic space telescopes.
Post by: TakeOff on 05/14/2017 06:45 PM
Just imagine, an habitable planet that doesn't need to be terraformed ... because it's already teeming with lush plant life. Send seed ships with human eggs and sperm, make of it a Second Earth. Ethical to do this to another biosphere? I guess not. Anyway, cost is prohibitive and First Earth gets no return on investment after bankrupting itself to stage the mission. So, probably never happen.

That would be unlikely. Even here on Earth we've had about today's oxygen level only 1/10 of the planet's history. And we might've problems with the microbiomes available before we evolved here. I think we are extremely tightly integrated with Earth as it is now and will have to construct our own environment in other places.
Post by: TakeOff on 05/14/2017 06:56 PM
Life on exoplanets may be detected sooner than we think, if this proposal comes to fruition: https://www.nasa.gov/directorates/spacetech/niac/2017_Phase_I_Phase_II/Solar_Gravity_Lens_Mission/

Travel to 550 AU to be able to observe a single target? Because steering this telescope would be... difficult, to say the least.
The LISA space laser interferometer is expected to perform an even greater miracle of precision flying. Solar gravity lensing is one of the "resources" that could be taken advantage of from early almost-interstellar flight. Other opportunities might be huge baseline parallax distance measurements and maybe radio interferometry, besides flying by distant objects and studying the interstellar medium. I think that a single object like an interesting exoplanet or the SMBH could be well worth a dedicated observatory.
Post by: hop on 05/14/2017 07:22 PM
The LISA space laser interferometer is expected to perform an even greater miracle of precision flying.
Precision distance measurement between active spacecraft is not equivalent to precision pointing, so it's a *different* miracle rather than a greater one. But of all the miracles required to make gravitational focus telescope work, pointing probably isn't the biggest.

If we find a planet with the right atmosphere (i.e. Earth-like), such a mission could certainly be worth it. I'm not aware of any other method that could deliver a 1000x1000px image of an exoplanet other than truly gigantic space telescopes.
It's not clear a gravitational focus telescope can actually do this in practice either. See https://arxiv.org/abs/1604.06351

Post by: CuddlyRocket on 05/16/2017 08:30 PM
K2-106, a system containing a metal rich planet and a planet of lower density (arXiv) (https://arxiv.org/pdf/1705.04163.pdf)

Quote
The two planets have similar masses, though very different densities. For K2-106b we derive Mp = 7.69 ± 0.82 M⊕, Rp = 1.52 ± 0.16 R⊕, and a high density of 12.0 +4.8 −3.2 g cm−3. For K2-106c, we find 6.79 ± 2.29 M⊕, Rp = 2.59 ± 0.27 R⊕ and a relatively low density of 2.4 +1.6 −1.1 g cm−3.

The 'Fulton Gap' has been proposed to be used to distinguish between 'super-Earths' and 'sub-Neptunes' - with the former having a radius of 1-1.75 R⊕ and the latter one of 1.75–3.5 R⊕. On that definition, this is an interesting system where the super-Earth is more massive than the sub-Neptune!
Post by: Star One on 05/16/2017 10:10 PM
New 'styrofoam' planet provides tools in search for habitable planets

https://m.phys.org/news/2017-05-styrofoam-planet-tools-habitable-planets.html
Post by: Star One on 05/25/2017 07:15 PM
Newly Found Exoplanet May Have Ring System Dwarfing Saturn’s

If confirmed, the  world’s rings would be some 200 times wider than Saturn’s and could reveal clues to our solar system’s early history

https://www.scientificamerican.com/article/newly-found-exoplanet-may-have-ring-system-dwarfing-saturn-rsquo-s/
Post by: Star One on 05/30/2017 11:28 AM
Astronomers discover 'super-Earth' planet orbiting nearby star

Quote
Abstract
We report the discovery of a super-Earth orbiting at the inner edge of the habitable zone of the star GJ 625 based on the analysis of the radial-velocity (RV) time series from the HARPS-N spectrograph, consisting in 151 HARPS-N measurements taken over 3.5 yr. GJ 625 b is a planet with a minimum mass M sin i of 2.82 ± 0.51 M⊕ with an orbital period of 14.628 ± 0.013 days at a distance of 0.078 AU of its parent star. The host star is the quiet M2 V star GJ 625, located at 6.5 pc from the Sun. We find the presence of a second radial velocity signal in the range 74-85 days that we relate to stellar rotation after analysing the time series of Ca II H&K and Hα spectroscopic indicators, the variations of the FWHM of the CCF and and the APT2 photometric light curves. We find no evidence linking the short period radial velocity signal to any activity proxy.

https://m.phys.org/news/2017-05-astronomers-super-earth-planet-orbiting-nearby.html
Post by: hop on 05/30/2017 09:57 PM
More fuel for the M-dwarf tidal locking debate:

On the Spin States of Habitable Zone Exoplanets Around M Dwarfs:The Effect of a Near-Resonant Companion (https://arxiv.org/abs/1705.09685) Alec M. Vinson, Brad M.S. Hansen

Quote
One longstanding problem for the potential habitability of planets within M dwarf systems is their likelihood to be tidally locked in a synchronously rotating spin state. This problem thus far has largely been addressed only by considering two objects: the star and the planet itself. However, many systems have been found to harbor multiple planets, with some in or very near to mean-motion resonances. The presence of a planetary companion near a mean-motion resonance can induce oscillatory variations in the mean-motion of the planet, which we demonstrate can have significant effects on the spin-state of an otherwise synchronously rotating planet. In particular, we find that a planetary companion near a mean-motion resonance can excite the spin states of planets in the habitable zone of small, cool stars, pushing otherwise synchronously rotating planets into higher amplitude librations of the spin state, or even complete circulation resulting in effective stellar days with full surface coverage on the order of years or decades. This increase in illuminated area can have potentially dramatic influences on climate, and thus on habitability. We also find that the resultant spin state can be very sensitive to initial conditions due to the chaotic nature of the spin state at early times within certain regimes. We apply our model to two hypothetical planetary systems inspired by the K00255 and TRAPPIST-1 systems, which both have Earth-sized planets in mean-motion resonances orbiting cool stars.
Post by: CuddlyRocket on 05/31/2017 12:30 AM
Astronomers discover 'super-Earth' planet orbiting nearby star

Quote
Abstract
We report the discovery of a super-Earth ... with a minimum mass M sin i of 2.82 ± 0.51 M⊕ ...

https://m.phys.org/news/2017-05-astronomers-super-earth-planet-orbiting-nearby.html

The authors have classified this as a super-Earth on the basis that its mass is between that of Earth and Neptune. I get the impression that most astronomers in the field would consider that definition to be overly-broad, with objects at the upper end of that mass range being referred to as mini-Neptunes instead. The authors do note that the term super-Earth "is also used by astronomers to describe planets bigger than Earth but smaller than the so-called "mini-Neptunes" (with a radius between two to four Earth-radii)."

Is there a confusion between definitions of super-Earths/mini-Neptunes based on mass and those based on the radius? Do astronomers using radial velocity techniques, which gives the mass, differ from their colleagues using transit techniques, which gives the radius?

If this object has the same average density as the Earth, its radius (x sin i) would be 1.41 times that of Earth, which is below the super-Earth/mini-Neptune boundary at 1.75 Earth radii based on the so-called 'Fulton Gap'. However, this is above the boundary based on the transition in the mass-radius relation identified by Chen and Kipping. A borderline case!
Post by: Star One on 06/02/2017 07:14 PM
Citizen scientists uncover a cold new world near sun

Quote
A new citizen-science tool released earlier this year to help astronomers pinpoint new worlds lurking in the outer reaches of our solar system has already led to a discovery: a brown dwarf a little more than 100 light years away from the Sun. Just six days after the launch of the Backyard Worlds: Planet 9 website in February, four different users alerted the science team to the curious object, whose presence has since been confirmed via an infrared telescope. Details were recently published in the Astrophysical Journal Letters.

Quote
"It's possible that there is a cold world closer than what we believe to be the closest star to the Sun," Faherty said. "Given enough time, I think our volunteers are going help to complete the map of our solar neighborhood."

https://phys.org/news/2017-06-citizen-scientists-uncover-cold-world.amp
Post by: Star One on 06/05/2017 04:16 PM
Meet KELT-9b, the Hottest Exoplanet Ever Discovered

The exoplanet’s host star blasts it with so much radiation that it will someday evaporate.

Quote
KELT-9b may just be the weirdest exoplanet astronomer Scott Gaudi has ever found. Gaudi, a researcher at The Ohio State University in Columbus, is the lead author of a paper published today in Nature describing the newly discovered hot, gassy exoplanet that is 3 times the size of Jupiter and located 650 light-years away from Earth.

The newly found exoplanet is tidally locked to its host star, meaning one side eternally faces a blast of radiant heat, Gaudi said. The 4300°C temperature of KELT-9b’s “dayside” is only about 1000°C cooler than the surface of our Sun.

If all of KELT-9b were this hot rather than just the dayside, it could be a star. But it still falls short of that classification because it doesn’t heat itself by means of hydrogen fusion. Instead, its heat comes from the intense radiation from its nearby host star, KELT-9.

https://eos.org/articles/meet-kelt-9b-the-hottest-exoplanet-ever-discovered

Weirdly it's in a polar orbit around its star.
Post by: Star One on 06/08/2017 07:19 PM
Relevant to any exoplanets in orbit around them.

Ultraviolet Insights into Red Dwarf Flares

https://www.centauri-dreams.org/?p=37914
Post by: Star One on 06/09/2017 04:51 PM
Planet Formation around TRAPPIST-1

https://www.centauri-dreams.org/?p=37917
Post by: CuddlyRocket on 06/13/2017 02:44 AM
Two new massive planets detected around the star HD 27894 (https://phys.org/news/2017-06-massive-planets-star-hd.html) (Phys.org article).
Three planets around HD 27894 (https://arxiv.org/pdf/1706.00509.pdf) (arXiv paper).

Quote
(Abstract)
Aims. Our new program with HARPS aims to detect mean motion resonant planetary systems around stars which were previously reported to have a single bona fide planet, often based only on sparse radial velocity data.
Methods. Archival and new HARPS radial velocities for the K2V star HD 27894 were combined and fitted with a three-planet self-consistent dynamical model. The best-fit orbit was tested for long-term stability.
Results. We find clear evidence that HD 27894 is hosting at least three massive planets. In addition to the already known Jovian planet with a period Pb ≈ 18 days we discover a Saturn-mass planet with Pc ≈ 36 days, likely in a 2:1 mean motion resonance with the first planet, and a cold massive planet (≈ 5.3 MJup) with a period Pd ≈ 5170 days on a moderately eccentric orbit (ed = 0.39).
Conclusions. HD 27894 is hosting a massive, eccentric giant planet orbiting around a tightly packed inner pair of massive planets likely involved in an asymmetric 2:1 mean motion resonance. HD 27894 may be an important milestone for probing planetary formation and evolution scenarios.
Post by: Star One on 06/13/2017 08:24 AM
I still can't help wonder if there are more planets in the large gap.
Post by: Bynaus on 06/13/2017 08:36 AM
Sounds like a 55 Cancri analogue system. A few gas giants on closely packed orbits, with a large, slightly eccentric jovian at ca. 5 AU. The resonance of the innermost two jovians at 55 Cnc is closer to 3:1, and there are more known planets in the 55 Cnc system (a hot super-Earth and a light-weight gas giant in the "gap"), but the similarities are striking (surprisingly, the authors do not mention that in their paper).
Post by: Star One on 06/13/2017 08:35 PM
New evidence that all stars are born in pairs

Quote
Did our sun have a twin when it was born 4.5 billion years ago?

Almost certainly yes — though not an identical twin. And so did every other sunlike star in the universe, according to a new analysis by a theoretical physicist from the University of California, Berkeley, and a radio astronomer from the Smithsonian Astrophysical Observatory at Harvard University.

Many stars have companions, including our nearest neighbor, Alpha Centauri, a triplet system. Astronomers have long sought an explanation. Are binary and triplet star systems born that way? Did one star capture another? Do binary stars sometimes split up and become single stars?

Astonomers have even searched for a companion to our sun, a star dubbed Nemesis because it was supposed to have kicked an asteroid into Earth’s orbit that collided with our planet and exterminated the dinosaurs. It has never been found.

The new assertion is based on a radio survey of a giant molecular cloud filled with recently formed stars in the constellation Perseus, and a mathematical model that can explain the Perseus observations only if all sunlike stars are born with a companion.

“We are saying, yes, there probably was a Nemesis, a long time ago,” said co-author Steven Stahler, a UC Berkeley research astronomer.

“We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries. These systems then either shrink or break apart within a million years.”

http://news.berkeley.edu/2017/06/13/new-evidence-that-all-stars-are-born-in-pairs/
Post by: Star One on 06/14/2017 07:46 PM
Mistaken brown dwarf is actually two planets orbiting each other

Quote
Finding massive planets is nothing new these days. But finding them orbiting each other instead of orbiting a star is unprecedented. An object initially thought to be a single brown dwarf is actually a pair of giant worlds. It’s not yet clear how this binary system formed, but the discovery may help redefine the line between planets and brown dwarfs – failed stars with tens of times the mass of Jupiter.

This pair of planets is made up of two balls of gas the size of Jupiter but almost four times more massive, separated by some 600 million kilometres, and slowly circling each other once per century or so. The young couple only emits light at infrared wavelengths, with residual heat from their formation, just 10 million years ago.

Observations with the 10-metre Keck II telescope, by a team led by William Best of the University of Hawaii, uncovered the binary system, with the help of adaptive optics that correct for the blurring effects of Earth’s atmosphere.

https://www.newscientist.com/article/2134712-mistaken-brown-dwarf-is-actually-two-planets-orbiting-each-other
Post by: CuddlyRocket on 06/14/2017 11:51 PM
Quote
But are they really planets? Maybe not. In the past, the dividing line between planets and brown dwarfs was generally placed at 14 Jupiter masses, when nuclear fusion of deuterium in the object’s core sets in.

But Latham argues that the best way to distinguish between the two is not by their mass but by how they form: brown dwarfs result from collapsing clouds of gas and dust, while planets form out of a stellar disk.

I think a lot (most, probably) of astronomers who have an opinion would say that these are not planets because they don't orbit a star or stellar remnant. But they're probably not rogue planets either, because it seems unlikely they were ejected from a stellar system as a binary couple. The problem with Latham's suggestion would seem to be how do you tell the difference between a solo brown dwarf and a solo rogue planet? And is there a minimum size, or is every pebble a brown dwarf? (Though this may not matter in practice as it would probably be difficult to detect anything smaller than a gas giant.)
Post by: clongton on 06/16/2017 12:20 AM
... how do you tell the difference between a solo brown dwarf and a solo rogue planet?

I suspect that would be the core temperature. A brown dwarf would be quite a bit warmer than a rogue planet, even a rocky one with a molten core.
Post by: jebbo on 06/19/2017 09:37 AM
An announcement from the Pale Red Dot team is expected at 11am CET:

Almost certainly to do with their Barnard's Star campaign (which started a couple of months ago)

--- Tony
Post by: Alpha_Centauri on 06/19/2017 10:22 AM
Sounds like it is just announcing the search rather than any discoveries yet.
Post by: jebbo on 06/19/2017 10:40 AM
Yes.  Search started on June 15th. I got the impression from one of the team that they started looking at Barnard's Star earlier, but apparently not.

They will also be looking at Ross 154 (a flare star).  Home to "Glory Station" in Cherryh's Alliance/Union setting.

--- Tony
Post by: Star One on 06/19/2017 10:49 AM
Sounds like it is just announcing the search rather than any discoveries yet.

I was under the impression there has been an ongoing examination of Barnard's star?

Yes.  Search started on June 15th. I got the impression from one of the team that they started looking at Barnard's Star earlier, but apparently not.

They will also be looking at Ross 154 (a flare star).  Home to "Glory Station" in Cherryh's Alliance/Union setting.

--- Tony

Seems a bit pointless to prioritise a flare star in the search.
Post by: Alpha_Centauri on 06/19/2017 10:56 AM
Proxima is a flare star too, many M dwarfs are.  It's the occupational hazard.

Speaking of which they will also be observing Proxima again for further planets.  Data to be released in real-time.
Post by: jebbo on 06/19/2017 11:03 AM
Seems a bit pointless to prioritise a flare star in the search.

Why? The point of this is to find the nearest planets (i.e. that are the most susceptible to follow-up).

Flare stars (well all M dwarfs really) are a bit problematic for habitability, but - depending on the initial water fraction - it is not ruled out.

--- Tony
Post by: Star One on 06/19/2017 11:20 AM
Seems a bit pointless to prioritise a flare star in the search.

Why? The point of this is to find the nearest planets (i.e. that are the most susceptible to follow-up).

Flare stars (well all M dwarfs really) are a bit problematic for habitability, but - depending on the initial water fraction - it is not ruled out.

--- Tony

I assumed obviously mistakenly by the fact that the OP classed it as a flare star that they were indicating that even amongst M dwarfs it's was very active, otherwise why mention it?
Post by: jebbo on 06/19/2017 11:55 AM
I assumed obviously mistakenly by the fact that the OP classed it as a flare star that they were indicating that even amongst M dwarfs it's was very active, otherwise why mention it?

It is more active than most - it is a UV Ceti type star, with major flares every couple of days or so - which I thought worth mentioning, that's all.

Its age is thought to be <1Gyr so it is a fairly young star, but this age is poorly constrained (gyrochronology!), and M dwarfs become less active with age.

And from a different angle, looking at active flare stars will help us understand the effects of flares.

--- Tony
Post by: Star One on 06/19/2017 12:02 PM
As a general point are they going to try and tie down Proxima C which I believe is meant to be a larger planet further out than b?
Post by: jebbo on 06/19/2017 12:25 PM
As a general point are they going to try and tie down Proxima C which I believe is meant to be a larger planet further out than b?

The ESO presser talks about more than one terrestrial sized planet, and there is a linear trend in the Proxima b RV data, so it will help. But whether the campaign will be long enough to confirm a "c" and its period is another question

Edit: there are variations in the 200-300 days and ~40day periods as well. A post is forthcoming on their website.

--- Tony
Post by: Star One on 06/19/2017 08:34 PM
Article on the same.

Pale Red Dot: Campaign 2

https://www.centauri-dreams.org/?p=37964
Post by: CuddlyRocket on 06/20/2017 06:11 AM

NASA Releases Kepler Survey Catalog with Hundreds of New Planet Candidates
Here is the briefing material ... [and] the archived video of the press conference:

Quote
... precise measurements of thousands of planets, [reveals] two distinct groups of small planets ... a clean division in the sizes of rocky, Earth-size planets and gaseous planets smaller than Neptune. Few planets were found between those groupings. ...

“We like to think of this study as classifying planets in the same way that biologists identify new species of animals,” said Benjamin Fulton, doctoral candidate at the University of Hawaii in Manoa, and lead author of the second study. “Finding two distinct groups of exoplanets is like discovering mammals and lizards make up distinct branches of a family tree.”

It seems that nature commonly makes rocky planets up to about 75 percent bigger than Earth. For reasons scientists don't yet understand, about half of those planets take on a small amount of hydrogen and helium that dramatically swells their size, allowing them to "jump the gap" and join the population closer to Neptune’s size.

This is what is being called by some (not Benjamin - though he possibly doesn't object! :) ) the Fulton Gap. He gives an explanation in the video as to why it might arise.
Post by: jebbo on 06/20/2017 10:36 AM
This is what is being called by some (not Benjamin - though he possibly doesn't object! :) ) the Fulton Gap. He gives an explanation in the video as to why it might arise.

The original paper is here https://arxiv.org/abs/1703.10375 (https://arxiv.org/abs/1703.10375), and predates the latest DR25 release.

The gap is also known as the "photoevaporation desert" ;-)

--- Tony

Post by: Alpha_Centauri on 06/20/2017 11:16 AM
The photoevaporation desert and the Fulton gap are separate as far as I know. You can see this in the bottom diagram page 12. The photoevaporation desert is the noticeable lack of Neptunes in the very highest insolations, top left. The Fulton gap is the distinct relatively low occurrence gap marked by the crossing point between the two lines denoting the atmospheric loss and gas poor models (the point being the data did not rule out either cause).
Post by: jebbo on 06/20/2017 12:25 PM
You are quite right! I should have re-read the paper as I clearly misremembered it.  What I should have said was "photoevaporation valley", which has two competing theories on cause.

The joys of getting up at 5:30am with insufficient coffee :-)

--- Tony
Post by: Alpha_Centauri on 06/20/2017 12:52 PM
I would say you are forgiven, but then again no one is allowed to be wrong on the internet.  :P
Post by: Star One on 06/20/2017 07:03 PM
A New Classification Scheme for Kepler Planets

https://www.centauri-dreams.org/?p=37972

This seems to make an indirect case for planet nine being as that's meant to be our missing mini-Neptune.
Post by: Star One on 06/23/2017 08:52 PM
A Partly Cloudy Exoplanet

http://www.skyandtelescope.com/astronomy-news/a-partly-cloudy-exoplanet/
Post by: Star One on 06/27/2017 10:56 AM
Betelgeuse captured by ALMA

Quote
This orange blob shows the nearby star Betelgeuse, as seen by the Atacama Large Millimeter/submillimeter Array (ALMA). This is the first time that ALMA has ever observed the surface of a star and this first attempt has resulted in the highest-resolution image of Betelgeuse available.

Betelgeuse is one of the largest stars currently known — with a radius around 1400 times larger than the Sun’s in the millimeter continuum. About 600 light-years away in the constellation of Orion (The Hunter), the red supergiant burns brightly, causing it to have only a short life expectancy. The star is just about eight million years old, but is already on the verge of becoming a supernova. When that happens, the resulting explosion will be visible from Earth, even in broad daylight.

The star has been observed in many other wavelengths, particularly in the visible, infrared, and ultraviolet. Using ESO’s Very Large Telescope astronomers discovered a vast plume of gas almost as large as our Solar System. Astronomers have also found a gigantic bubble that boils away on Betelgeuse’s surface. These features help to explain how the star is shedding gas and dust at tremendous rates (eso0927, eso1121). In this picture, ALMA observes the hot gas of the lower chromosphere of Betelgeuse at sub-millimeter wavelengths — where localised increased temperatures explain why it is not symmetric. Scientifically, ALMA can help us to understand the extended atmospheres of these hot, blazing stars.
Post by: CuddlyRocket on 06/27/2017 10:23 PM
Betelgeuse captured by ALMA (link to ESO webpage, including images) (http://www.eso.org/public/unitedkingdom/images/potw1726a/)
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 06/28/2017 09:47 AM
Groundbreaking discovery confirms existence of orbiting supermassive black holes

Quote
For the first time ever, astronomers at The University of New Mexico say they've been able to observe and measure the orbital motion between two supermassive black holes hundreds of millions of light years from Earth - a discovery more than a decade in the making.
UNM Department of Physics & Astronomy graduate student Karishma Bansal is the first-author on the paper, 'Constraining the Orbit of the Supermassive Black Hole Binary 0402+379', recently published in The Astrophysical Journal. She, along with UNM Professor Greg Taylor and colleagues at Stanford, the U.S. Naval Observatory and the Gemini Observatory, have been studying the interaction between these black holes for 12 years.
"For a long time, we've been looking into space to try and find a pair of these supermassive black holes orbiting as a result of two galaxies merging," said Taylor. "Even though we've theorized that this should be happening, nobody had ever seen it until now."
In early 2016, an international team of researchers, including a UNM alumnus, working on the LIGO project detected the existence of gravitational waves, confirming Albert Einstein's 100-year-old prediction and astonishing the scientific community. These gravitational waves were the result two stellar mass black holes (~30 solar mass) colliding in space within the Hubble time. Now, thanks to this latest research, scientists will be able to start to understand what leads up to the merger of supermassive black holes that creates ripples in the fabric of space-time and begin to learn more about the evolution of galaxies and the role these black holes play in it.
Using the Very Long Baseline Array (VLBA), a system made up of 10 radio telescopes across the U.S. and operated in Socorro, N.M., researchers have been able to observe several frequencies of radio signals emitted by these supermassive black holes (SMBH). Over time, astronomers have essentially been able to plot their trajectory and confirm them as a visual binary system. In other words, they've observed these black holes in orbit with one another.

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/04/2017 04:12 PM
Probability of CME Impact on Exoplanets Orbiting M Dwarfs and Solar-Like Stars

Quote
Solar coronal mass ejections (CMEs) produce adverse space weather effects at Earth. Planets in the close habitable zone of magnetically active M dwarfs may experience more extreme space weather than at Earth, including frequent CME impacts leading to atmospheric erosion and leaving the surface exposed to extreme flare activity. Similar erosion may occur for hot Jupiters with close orbits around solar-like stars. We have developed a model, Forecasting a CME's Altered Trajectory (ForeCAT), which predicts a CME's deflection. We adapt ForeCAT to simulate CME deflections for the mid-type M dwarf V374 Peg and hot Jupiters with solar-type hosts. V374 Peg's strong magnetic fields can trap CMEs at the M dwarfs's Astrospheric Current Sheet, the location of the minimum in the background magnetic field. Solar-type CMEs behave similarly, but have much smaller deflections and do not get trapped at the Astrospheric Current Sheet. The probability of planetary impact decreases with increasing inclination of the planetary orbit with respect to the Astrospheric Current Sheet - 0.5 to 5 CME impacts per day for M dwarf exoplanets, 0.05 to 0.5 CME impacts per day for solar-type hot Jupiters. We determine the minimum planetary magnetic field necessary to shield a planet's atmosphere from the CME impacts. M dwarf exoplanets require values between tens and hundreds of Gauss. Hot Jupiters around a solar-type star, however, require a more reasonable <30 G. These values exceed the magnitude required to shield a planet from the stellar wind, suggesting CMEs may be the key driver of atmospheric losses.

https://arxiv.org/abs/1605.02683
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/04/2017 07:24 PM
Isotope shift and search for metastable superheavy elements in astrophysical data

Quote
Spectral lines belonging to the short-lifetime heavy radioactive elements up to Es (Z=99) have been found in the spectra of the Przybylski's star. We suggest that these unstable elements may be decay products of a "magic" metastable nucleus belonging to the the island of stability where the nuclei have a magic number of neutrons N=184. The laboratory-produced nuclei have a significantly smaller number of neutrons. To identify spectra of the N=184 isotopes of these nuclei and their neutron-reach superheavy decay products in astrophysical data we calculate the isotope shift which should be added to the laboratory - measured wavelenghs. The results for the isotopic shifts in the strongest optical electromagnetic transitions in No, Lr, Nh, Fl,and Z=120 elements are presented.

https://arxiv.org/abs/1703.04250
Post by: Star One on 07/06/2017 07:41 PM
A cosmic barbecue: Researchers spot 60 new 'hot Jupiter' candidates

Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 07/07/2017 05:40 AM
^^ Paper on arXiv (https://arxiv.org/abs/1706.06602)

Interesting new technique for finding exoplanets, relying on an increase in light flux from a stellar system due to the added light reflected from the exoplanets, rather than a decrease due to a transit. The authors note that their technique needs to be validated by corroboration using doppler measurements, but if it is then it could also be used on other databases of light flux.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/07/2017 06:59 AM
^^ Paper on arXiv (https://arxiv.org/abs/1706.06602)

Interesting new technique for finding exoplanets, relying on an increase in light flux from a stellar system due to the added light reflected from the exoplanets, rather than a decrease due to a transit. The authors note that their technique needs to be validated by corroboration using doppler measurements, but if it is then it could also be used on other databases of light flux.
Isn't that paper directly related to the finding of those 60 hot Jupiter candidates covered in the article I posted directly above your post?
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/07/2017 03:50 PM
The low-mass content of the massive young star cluster RCW 38

Quote
RCW 38 is a deeply embedded young (~1 Myr), massive star cluster located at a distance of 1.7 kpc. Twice as dense as the Orion Nebula Cluster, orders of magnitude denser than other nearby star forming regions, and rich in massive stars, RCW 38 is an ideal place to look for potential differences in brown dwarf formation efficiency as a function of environment. We present deep, high resolution adaptive optics data of the central ~0.5x0.5 pc^2 obtained with NACO at the Very Large Telescope. Through comparison with evolutionary models we determine masses and extinction for ~480 candidate members, and derive the first Initial Mass Function (IMF) of the cluster extending into the substellar regime. Representing the IMF as a set of power laws in the form dN/dM~M^(-alpha), we derive the slope alpha = 1.60+-0.13 for the mass range 0.5 - 20 MSun which is shallower than the Salpeter slope, but in agreement with results in several other young massive clusters. At the low-mass side, we find alpha = 0.71+-0.11 for masses between 0.02 and 0.5 MSun, or alpha = 0.81+-0.08 for masses between 0.02 and 1 MSun. Our result is in agreement with the values found in other young star-forming regions, revealing no evidence that a combination of high stellar densities and the presence of numerous massive stars affect the formation efficiency of brown dwarfs and very-low mass stars. We estimate that the Milky Way galaxy contains between 25 and 100 billion brown dwarfs (with masses > 0.03 MSun).

https://arxiv.org/abs/1707.00277
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 07/09/2017 07:57 PM
^^ Paper on arXiv (https://arxiv.org/abs/1706.06602)

Interesting new technique for finding exoplanets, relying on an increase in light flux from a stellar system due to the added light reflected from the exoplanets, rather than a decrease due to a transit. The authors note that their technique needs to be validated by corroboration using doppler measurements, but if it is then it could also be used on other databases of light flux.
Isn't that paper directly related to the finding of those 60 hot Jupiter candidates covered in the article I posted directly above your post?

Yes. Hence the two up-arrows at the beginning of my post, which is forum-speak for 'refers to previous post'.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/09/2017 07:59 PM
^^ Paper on arXiv (https://arxiv.org/abs/1706.06602)

Interesting new technique for finding exoplanets, relying on an increase in light flux from a stellar system due to the added light reflected from the exoplanets, rather than a decrease due to a transit. The authors note that their technique needs to be validated by corroboration using doppler measurements, but if it is then it could also be used on other databases of light flux.
Isn't that paper directly related to the finding of those 60 hot Jupiter candidates covered in the article I posted directly above your post?

Yes. Hence the two up-arrows at the beginning of my post, which is forum-speak for 'refers to previous post'.

I missed those using Tapatalk hence the post. So sorry about that.
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 07/11/2017 04:59 AM
- 2 up-arrows :) -

No problem. I could've just quoted you or spelt things out - but I was being unnecessarily concise, or lazy, or some combination thereof!
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/12/2017 09:04 AM
Hidden Stars May Make Planets Appear Smaller

Quote
In the search for planets similar to our own, an important point of comparison is the planet's density. A low density tells scientists a planet is more likely to be gaseous like Jupiter, and a high density is associated with rocky planets like Earth. But a new study suggests some are less dense than previously thought because of a second, hidden star in their systems.

As telescopes stare at particular patches of sky, they can't always differentiate between one star and two. A system of two closely orbiting stars may appear in images as a single point of light, even from sophisticated observatories such as NASA's Kepler space telescope. This can have significant consequences for determining the sizes of planets that orbit just one of these stars, says a forthcoming study in the Astronomical Journal by Elise Furlan of Caltech/IPAC-NExScI in Pasadena, California, and Steve Howell at NASA's Ames Research Center in California's Silicon Valley.

"Our understanding of how many planets are small like Earth, and how many are big like Jupiter, may change as we gain more information about the stars they orbit," Furlan said. "You really have to know the star well to get a good handle on the properties of its planets."

Some of the most well-studied planets outside our solar system -- or exoplanets -- are known to orbit lone stars. We know Kepler-186f, an Earth-size planet in the habitable zone of its star, orbits a star that has no companion (the habitable zone is the distance at which a rocky planet could support liquid water on its surface). TRAPPIST-1, the ultra-cool dwarf star that is home to seven Earth-size planets, does not have a companion either. That means there is no second star complicating the estimation of the planets' diameters, and therefore their densities.

But other stars have a nearby companion, high-resolution imaging has recently revealed. David Ciardi, chief scientist at the NASA Exoplanet Science Institute (NExScI) at Caltech, led a large-scale effort to follow up on stars that Kepler had studied using a variety of ground-based telescopes. This, combined with other research, has confirmed that many of the stars where Kepler found planets have binary companions. In some cases, the diameters of the planets orbiting these stars were calculated without taking the companion star into consideration. That means estimates for their sizes should be smaller, and their densities higher, than their true values.

Previous studies determined that roughly half of all the sun-like stars in our sun's neighborhood have a companion within 10,000 astronomical units (an astronomical unit is equal to the average distance between the sun and Earth, 93 million miles or 150 million kilometers). Based on this, about 15 percent of stars in the Kepler field could have a bright, close companion -- meaning planets around these stars may be less dense than previously thought.

The Transit Problem for Binaries

When a telescope spots a planet crossing in front of its star -- an event called a "transit" -- astronomers measure the resulting apparent decrease in the star's brightness. The amount of light blocked during a transit depends on the size of the planet -- the bigger the planet, the more light it blocks, and the greater the dimming that is observed. Scientists use this information to determine the radius -- half the diameter -- of the planet.

If there are two stars in the system, the telescope measures the combined light of both stars. But a planet orbiting one of these stars will cause just one of them to dim. So, if you don't know that there is a second star, you will underestimate the size of the planet.

For example, if a telescope observes that a star dims by 5 percent, scientists would determine the transiting planet's size relative to that one star. But if a second star adds its light, the planet must be larger to cause the same amount of dimming.

If the planet orbits the brighter star in a binary pair, most of the light in the system comes from that star anyway, so the second star won't have a big effect on the planet's calculated size. But if the planet orbits the fainter star, the larger, primary star contributes more light to the system, and the correction to the calculated planet radius can be large -- it could double, triple or increase even more. This will affect how the planet's orbital distance is calculated, which could impact whether the planet is found to be in the habitable zone.

If the stars are roughly equal in brightness, the "new" radius of the planet is about 40 percent larger than if the light were assumed to come from a single star. Because density is calculated using the cube of the radius, this would mean a nearly three-fold decrease in density. The impact of this correction is most significant for smaller planets because it means a planet that had once been considered rocky could, in fact, be gaseous.

The New Study

In the new study, Furlan and Howell focused on 50 planets in the Kepler observatory's field of view whose masses and radii were previously estimated. These planets all orbit stars that have stellar companions within about 1,700 astronomical units. For 43 of the 50 planets, previous reports of their sizes did not take into account the contribution of light from a second star. That means a revision to their reported sizes is necessary.

In most cases, the change to the planets' reported sizes would be small. Previous research showed that 24 of the 50 planets orbit the bigger, brighter star in a binary pair. Moreover, Furlan and Howell determined that 11 of these planets would be too large to be planets if they orbited the fainter companion star. So, for 35 of the 50 planets, the published sizes will not change substantially.

But for 15 of the planets, they could not determine whether they orbit the fainter or the brighter star in a binary pair. For five of the 15 planets, the stars in question are of roughly equal brightness, so their densities will decrease substantially regardless of which star they orbit.

This effect of companion stars is important for scientists characterizing planets discovered by Kepler, which has found thousands of exoplanets. It will also be significant for NASA's upcoming Transiting Exoplanet Survey Satellite (TESS) mission, which will look for small planets around nearby, bright stars and small, cool stars.

"In further studies, we want to make sure we are observing the type and size of planet we believe we are," Howell said. "Correct planet sizes and densities are critical for future observations of high-value planets by NASA's James Webb Space Telescope. In the big picture, knowing which planets are small and rocky will help us understand how likely we are to find planets the size of our own elsewhere in the galaxy."

https://exoplanets.nasa.gov

https://www.jpl.nasa.gov/news/news.php?release=2017-187&rn=news.xml&rst=6893
Post by: Star One on 07/12/2017 01:17 PM
Eight planetary systems found hosting 20 super-Earth & Neptune-mass companions

Quote
A new treasure trove of planets, ranging from worlds with small masses and short orbital periods of less than 15 days to super-Earth-sized planets that can take up to a year to orbit their star, has been discovered by astronomers using the world’s most successful ground-based planet-finding instrument.

The 20 new worlds have been found around eight bright, Sun-like stars by the HARPS (High Accuracy Radial velocity Planet Searcher) Echelle Spectograph instrument, mounted on the 3.6m telescope at the European Southern Observatory in Chile. HARPS, which has discovered around 200 planets since 2003, is are able to measure the velocity of a star’s wobble incurred by the gravity of orbiting planets with the extreme precision of 1 m/s.

Quote
One of the systems observed was a binary system containing the stars HD 20781 and HD 20782. Although planets have been found in binary systems before, it is still uncertain how disruptive the gravitational tides from two stars can be to planet formation, or whether there could be long-term interactions between the two stars and their planets which make them unstable.

This system, however, is packed with planets. Orbiting around the star HD 201781 are two super-Earths with orbits of 5.3 and 13.9 days and two Neptune-mass planets with orbits of 29 and 86 days. The brighter star of the two, HD 20782, also has a Jupiter-sized world in an eccentric 595-day orbit.

Jason Dittman an astronomer at Harvard University was excited by the planets in the study and, in particular, this binary system. “These planets are really interesting because they have these longer orbital periods, and they complement the planets from transit surveys like Kepler. If we want a complete picture of what sort of planets exist in the universe, then discoveries like these are vital to the story,” he says.

Quote
Dittman believes that HARPS and other radial velocity surveys in general don’t get enough credit for the amount of time and dedication that goes into their observations.“Detecting planets with periods that are several years long takes a long time to do because you want to see the planet go around the star a couple of times.”

He continued, “The dedication and forward-thinking to get data on a star for many years is amazing. It’s great to see these long-running radial velocity programs continue to hit pay-dirt and find some longer period, eccentric systems with which to test our theories.”

https://astronomynow.com/2017/07/12/eight-planetary-systems-found-hosting-20-super-earth-neptune-mass-companions/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/12/2017 07:25 PM
Smallest-ever star discovered by astronomers

Quote
The smallest star yet measured has been discovered by a team of astronomers led by the University of Cambridge. With a size just a sliver larger than that of Saturn, the gravitational pull at its stellar surface is about 300 times stronger than what humans feel on Earth.

The star is likely as small as stars can possibly become, as it has just enough mass to enable the fusion of hydrogen nuclei into helium. If it were any smaller, the pressure at the centre of the star would no longer be sufficient to enable this process to take place. Hydrogen fusion is also what powers the Sun, and scientists are attempting to replicate it as a powerful energy source here on Earth.

These very small and dim stars are also the best possible candidates for detecting Earth-sized planets which can have liquid water on their surfaces, such as TRAPPIST-1, an ultracool dwarf surrounded by seven temperate Earth-sized worlds.

The newly-measured star, called EBLM J0555-57Ab, is located about 600 light-years away. It is part of a binary system, and was identified as it passed in front of its much larger companion, a method which is usually used to detect planets, not stars. Details will be published in the journal Astronomy & Astrophysics.

“Our discovery reveals how small stars can be,” said Alexander Boetticher, the lead author of the study, and a Master’s student at Cambridge’s Cavendish Laboratory and Institute of Astronomy. “Had this star formed with only a slightly lower mass, the fusion reaction of hydrogen in its core could not be sustained, and the star would instead have transformed into a brown dwarf.”

https://astronomynow.com/2017/07/12/smallest-ever-star-discovered-by-astronomers/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/13/2017 07:20 PM
More to Life Than the Habitable Zone

Quote
The teams, both led by researchers at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., say the behavior of the star in the TRAPPIST-1 system makes it much less likely than generally thought, that planets there could support life.

The TRAPPIST-1 star, a red dwarf, is much fainter and less massive than the Sun. It is rapidly spinning and generates energetic flares of ultraviolet (UV) radiation.

The first team, a pair of CfA theorists, considered many factors that could affect conditions on the surfaces of planets orbiting red dwarfs. For the TRAPPIST-1 system they looked at how temperature could have an impact on ecology and evolution, plus whether ultraviolet radiation from the central star might erode atmospheres around the seven planets surrounding it. These planets are all much closer to the star than the Earth is to the Sun, and three of them are located well within the habitable zone.

"The concept of a habitable zone is based on planets being in orbits where liquid water could exist," said Manasvi Lingam, a Harvard researcher who led the study. "This is only one factor, however, in determining whether a planet is hospitable for life."

Lingam and his co-author, Harvard professor Avi Loeb, found that planets in the TRAPPIST-1 system would be barraged by UV radiation with an intensity far greater than experienced by Earth.

"Because of the onslaught by the star's radiation, our results suggest the atmosphere on planets in the TRAPPIST-1 system would largely be destroyed," said Loeb. "This would hurt the chances of life forming or persisting."

Lingam and Loeb estimate that the chance of complex life existing on any of the three TRAPPIST-1 planets in the habitable zone is less than 1% of that for life existing on Earth.

In a separate study, another research team from the CfA and the University of Massachusetts in Lowell found that the star in TRAPPIST-1 poses another threat to life on planets surrounding it. Like the Sun, the red dwarf in TRAPPIST-1 is sending a stream of particles outwards into space. However, the pressure applied by the wind from TRAPPIST-1's star on its planets is 1,000 to 100,000 times greater than what the solar wind exerts on the Earth.

The authors argue that the star’s magnetic field will connect to the magnetic fields of any planets in orbit around it, allowing particles from the star’s wind to directly flow onto the planet’s atmosphere. If this flow of particles is strong enough, it could strip the planet's atmosphere and perhaps evaporate it entirely.

https://www.cfa.harvard.edu/news/2017-20
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/18/2017 07:40 PM
Why We Need a New Type of SETI Instrument

Quote
The SETI Institute has developed an instrument that, at relatively low cost, could continuously survey the entire night sky for brief laser pulses.  This is completely unlike the optical SETI efforts that have been made in the past, and continue to be made today: experiments that use sensitive photomultiplier detectors, but are limited to one star system at a time.  That’s akin to a radio SETI search able to only monitor a single frequency channel.  Extremely limited.

However, the Institute’s new Laser SETI instrument is not constrained in this way – it can look everywhere simultaneously.  The technology has been prototyped and subjected to preliminary tests, and consists of a robust assembly of straightforward optical and mechanical components.  It can be easily and inexpensively) replicated.

http://www.seti.org/why-we-need-a-new-type-of-seti-instrument
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/19/2017 07:04 PM
“Variable and polarized radio emission from the T6 brown dwarf WISEP J112254.73+255021.5”

Quote
But we do see a lot of complicated variability in the radio emission! What I found to be the most exciting was the measurement shown in the lowest panel of the figure above. It shows the level of circular polarization of the radio waves we get from WISE 1122+25. Almost all astronomical objects emit light that is unpolarized in the circular sense — that is, 0% circular polarization. Radio-emitting brown dwarfs are among the rare objects that can produce high levels of circular polarization. The way we quantify things, circular polarization levels can range between +100%, meaning fully right-handed circular polarization, to –100%, for fully left-handed circular polarization.

What’s neat about the VLA data is that the polarization fraction seems to swing back and forth between the two states. We’ve seen brown dwarfs emit radio bursts with both kinds of handedness, but I’m not aware of any data showing these kind of long-lasting, abrupt transitions. And if you get a bit ambitious in the interpretation, you can imagine that maybe this handedness flips back periodically with the rotation of the brown dwarf. Looking at the different pieces of data, we found some evidence for periodicity at 116 minutes. But the whole observation only spanned 162 minutes, so that’s a very tentative idea — you’d want to see multiple flips back and forth all in sequence to be more confident.

But … if you want to get even more ambitious … You might be able to explain that kind of behavior if this object has a magnetic field that has a major axis that’s very misaligned with the rotation axis. With the right viewing geometry and magnetic polar caps that emitted strongly polarized radiation, you can get curves that look similar to the data.

Post by: Star One on 07/19/2017 07:53 PM
Astronomers discover Earth-sized exoplanet with very short orbital period

Quote
An international team of astronomers has detected a new Earth-sized exoplanet in an ultra-short period around its parent star. The alien world, designated EPIC 228813918 b, circles its host every four hours and 20 minutes, which makes it the second-shortest orbital period of a planet known to date. The finding was presented in a paper published July 14 on arXiv.org.

Quote
The newly found planet is slightly smaller than Earth (0.89 Earth radii). However, it's extremely massive – its estimated maximum mass is 0.7 Jupiter masses. The exoplanet orbits an M-dwarf star nearly half the size and mass of our sun every 4.3 hours. The planetary system is located some 310 light years away from the Earth.

Quote
The researchers also managed to determine the chemical composition of EPIC 228813918 b. According to them, the planet has an iron core and a silicate mantle. The minimum iron mass fraction was found to be about 0.52, which is greater than that of Earth, Venus or Mars, but smaller than that of Mercury.

https://phys.org/news/2017-07-astronomers-earth-sized-exoplanet-short-orbital.amp
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 07/19/2017 08:26 PM
Quote
However, it's extremely massive – its estimated maximum mass is 0.7 Jupiter masses.

Complete BS (sorry). This is its 3-sigma upper limit mass, based on a full 5 data points... The authors use this figure only to show that the object is in the planetary mass regime (and is not, e.g., a white dwarf). Certainly, one cannot say from that observation alone that "its extremely massive".

Interestingly, they do calculate a minimum density for the planet (>6.4 g/cm3), which is given by the requirement that it orbits its star outside the Roche limit, and from this a minimum iron core fraction of 0.45 (higher than the Earth but lower than Mercury - but again, remember this is a lower limit).
Title: Re: Exoplanets And Stars Thread
Post by: as58 on 07/19/2017 09:12 PM
Complete BS (sorry). This is its 3-sigma upper limit mass, based on a full 5 data points... The authors use this figure only to show that the object is in the planetary mass regime (and is not, e.g., a white dwarf). Certainly, one cannot say from that observation alone that "its extremely massive".

That's some impressive misreporting by phys.org. The mass limit is not mentioned in the abstract, so they must've read the paper. Alas, apparently without understanding much.

edit: Some nitpicking, mass upper limit is based only on the two Keck/HIRES observations, which are much more accurate than Subaru/IRCS radial velocities.
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 07/20/2017 03:20 AM
Astronomers discover Earth-sized exoplanet with very short orbital period

From the arXiv paper (https://arxiv.org/abs/1707.04549):

Quote
For a stellar radius of 0.44 R and a radius ratio of ≈ 0.02, we derive a planetary radius of around 1.0 R⊕. For such a planet, we consider a very conservative upper-limit to the mass to be 3 M⊕ (Seager et al. 2007 predict a mass of around 2.7 M⊕ for a 1 R⊕ planet composed of solid iron).
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/26/2017 06:33 PM
Gamma-ray burst captured in unprecedented detail

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Data from multiple telescopes used to address long-standing questions about the universe's most powerful explosions

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Gamma-ray bursts are among the most energetic and explosive events in the universe. They are also short-lived, lasting from a few milliseconds to about a minute. This has made it tough for astronomers to observe a gamma-ray burst in detail. Using a wide array of ground- and space-based telescope observations, astronomers constructed one of the most detailed descriptions of a gamma-ray burst to date.

https://www.sciencedaily.com/releases/2017/07/170726132110.htm
Title: Re: Exoplanets And Stars Thread
Post by: hop on 07/26/2017 07:46 PM
Oops. It seems some "validated" planets are more valid than others
Disproval of the validated planets K2-78b, K2-82b, and K2-92b (https://arxiv.org/abs/1707.08007) (accepted for publication in A&A)
Quote
Transiting super-Earths orbiting bright stars in short orbital periods are interesting targets for the study of planetary atmospheres. While selecting super-Earths suitable for further characterization from the ground among a list of confirmed and validated exoplanets detected by K2, we found some suspicious cases that led to us re-assessing the nature of the detected transiting signal. We did a photometric analysis of the K2 light curves and centroid motions of the photometric barycenters. Our study shows that the validated planets K2-78b, K2-82b, and K2-92b are actually not planets but background eclipsing binaries. The eclipsing binaries are inside the Kepler photometric aperture, but outside the ground-based high resolution images used for validation. We advise extreme care on the validation of candidate planets discovered by space missions. It is important that all the assumptions in the validation process are carefully checked. An independent confirmation is mandatory in order to avoid wasting valuable resources on further characterization of non-existent targets.
Post by: Star One on 07/26/2017 09:02 PM
Oops. It seems some "validated" planets are more valid than others
Disproval of the validated planets K2-78b, K2-82b, and K2-92b (https://arxiv.org/abs/1707.08007) (accepted for publication in A&A)
Quote
Transiting super-Earths orbiting bright stars in short orbital periods are interesting targets for the study of planetary atmospheres. While selecting super-Earths suitable for further characterization from the ground among a list of confirmed and validated exoplanets detected by K2, we found some suspicious cases that led to us re-assessing the nature of the detected transiting signal. We did a photometric analysis of the K2 light curves and centroid motions of the photometric barycenters. Our study shows that the validated planets K2-78b, K2-82b, and K2-92b are actually not planets but background eclipsing binaries. The eclipsing binaries are inside the Kepler photometric aperture, but outside the ground-based high resolution images used for validation. We advise extreme care on the validation of candidate planets discovered by space missions. It is important that all the assumptions in the validation process are carefully checked. An independent confirmation is mandatory in order to avoid wasting valuable resources on further characterization of non-existent targets.

Isn't this paper rather stating the obvious and the last Kepler main mission release was done off the back of follow up ground observations.
Title: Re: Exoplanets And Stars Thread
Post by: hop on 07/27/2017 03:13 AM
Isn't this paper rather stating the obvious and the last Kepler main mission release was done off the back of follow up ground observations.
No. Relevant sentence from the abstract
Quote
The eclipsing binaries are inside the Kepler photometric aperture, but outside the ground-based high resolution images used for validation.
In other words, there was strong evidence of the EBs in the Kepler data, but the team that "validated" the planets didn't do the checks that would have caught them, and also didn't detect the EBs in their ground based follow up because they were outside the FOV.

From the discussion
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Our result shows that, though planet validation techniques are useful tools, great care needs to be taken to correctly validate candidate planets discovered by space missions. Crossfield et al. (2016) made a sound statistical study and a careful and detailed ground-based characterization of the targets, including high angular resolution imaging, but they failed to look for possible contaminants a few arcseconds away from the targets. In the cases mentioned above, the contaminants were too far away to be included in the field of view of the high resolution image and they were not considered further in the analysis.  The reliability of a statistical study is only as good as the understanding of the contamination sources. Here we show i) that validation methods applied to these targets by Crossfield et al.  (2016) underestimate the impact of background contaminants and consequently, ii) the planet likelihood estimates are not representative of the true nature of the candidates in these cases.

We insist that this is not the result of a failure of the design of the validation procedure, but the result of an incorrect assessment of the impact on the photometry of neighbouring sources. Our results can be used to improve the performance of planet validation techniques.
(emphasis in the original)

FWIW, the original paper reporting these ex-planets is https://arxiv.org/abs/1607.05263
Title: Re: Exoplanets And Stars Thread
Post by: Alpha_Centauri on 07/27/2017 03:45 AM
Super-Pandora? Candidate Neptune-sized exomoon potentially orbiting Superjovian Kepler-1625b.

HEK VI: On the Dearth of Galilean Analogs in Kepler and the Exomoon Candidate Kepler-1625b I
https://arxiv.org/pdf/1707.08563.pdf
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Finally, we have briefly highlighted our identification of an exomoon candidate in the Kepler-1625 system, for which we have secured a follow-up observation with HST. This candidate has passed a thorough preliminary inspection, but we emphasize again our position that the Kepler data are insufficient to make a conclusive statement about the existence of this moon. Only after the HST observation is made [October 2017] should any claim about this moon’s existence be given much credence.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/27/2017 07:09 AM
So what do they want them to do go through all the data from Kepler again, that will take years and no doubt cost a fair bit of money?
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 07/27/2017 07:49 AM
So what do they want them to do go through all the data from Kepler again, that will take years and no doubt cost a fair bit of money?

Who is they and them? The Kepler data are freely available.

Regarding the "super-Pandora", this is an exiting - potential - find. Such systems might be rare (just as Hot Jupiters turned out to be rare), but it would be no surprise that the first exomoon was indeed a somewhat exotic Jovian/Neptunian binary. Looking forward to the results coming from the upcoming HST observation.
Post by: Star One on 07/27/2017 08:12 AM
So what do they want them to do go through all the data from Kepler again, that will take years and no doubt cost a fair bit of money?

Who is they and them? The Kepler data are freely available.

Regarding the "super-Pandora", this is an exiting - potential - find. Such systems might be rare (just as Hot Jupiters turned out to be rare), but it would be no surprise that the first exomoon was indeed a somewhat exotic Jovian/Neptunian binary. Looking forward to the results coming from the upcoming HST observation.

The Kepler team, I assumed it would be obvious that's who I was referring to? After all how many groups are going to have the time and money to go through all that public data, money doesn't grow on trees these days.
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 07/27/2017 11:20 AM
So what do they want them to do go through all the data from Kepler again, that will take years and no doubt cost a fair bit of money?

Who is they and them? The Kepler data are freely available.

Regarding the "super-Pandora", this is an exiting - potential - find. Such systems might be rare (just as Hot Jupiters turned out to be rare), but it would be no surprise that the first exomoon was indeed a somewhat exotic Jovian/Neptunian binary. Looking forward to the results coming from the upcoming HST observation.

The Kepler team, I assumed it would be obvious that's who I was referring to? After all how many groups are going to have the time and money to go through all that public data, money doesn't grow on trees these days.

There is no expectation towards the core Kepler team involved here. Its also not like there is a "final word" on the Kepler data, either. Different researchers have been looking at the same data for many years now and the way these data have been reduced (how we go from raw data to exoplanet parameters) has been improved time and again, and will no doubt continue to happen in the future to some extent.

Looking for exomoons is also a completely different thing - and thus requires a different approach and data processing pipline (see the linked paper) - than to look for exoplanets. The funding for this kind of projects using publicly available data depends on the funding background of the individual researcher. In this case, Kipping is both a tenured professor at a university and probably has some external project funding from NSF, NASA or other sources.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/27/2017 11:28 AM
So what do they want them to do go through all the data from Kepler again, that will take years and no doubt cost a fair bit of money?

Who is they and them? The Kepler data are freely available.

Regarding the "super-Pandora", this is an exiting - potential - find. Such systems might be rare (just as Hot Jupiters turned out to be rare), but it would be no surprise that the first exomoon was indeed a somewhat exotic Jovian/Neptunian binary. Looking forward to the results coming from the upcoming HST observation.

The Kepler team, I assumed it would be obvious that's who I was referring to? After all how many groups are going to have the time and money to go through all that public data, money doesn't grow on trees these days.

There is no expectation towards the core Kepler team involved here. Its also not like there is a "final word" on the Kepler data, either. Different researchers have been looking at the same data for many years now and the way these data have been reduced (how we go from raw data to exoplanet parameters) has been improved time and again, and will no doubt continue to happen in the future to some extent.

Looking for exomoons is also a completely different thing - and thus requires a different approach and data processing pipline (see the linked paper) - than to look for exoplanets. The funding for this kind of projects using publicly available data depends on the funding background of the individual researcher. In this case, Kipping is both a tenured professor at a university and probably has some external project funding from NSF, NASA or other sources.

The only way I can see any group reanalysing all the Kepler data is if someone comes up with an algorithm to do all the heavy lifting.
Title: Re: Exoplanets And Stars Thread
Post by: Alpha_Centauri on 07/27/2017 11:31 AM
Lead author on the exomoon paper explains their rationale for publishing now;

https://blogs.scientificamerican.com/observations/are-astronomers-on-the-verge-of-finding-an-exomoon/
Title: Re: Exoplanets And Stars Thread
Post by: LouScheffer on 07/27/2017 01:53 PM
Oops. It seems some "validated" planets are more valid than others
Disproval of the validated planets K2-78b, K2-82b, and K2-92b (https://arxiv.org/abs/1707.08007) (accepted for publication in A&A)
Quote
[...] Our study shows that the validated planets K2-78b, K2-82b, and K2-92b are actually not planets but background eclipsing binaries. The eclipsing binaries are inside the Kepler photometric aperture, but outside the ground-based high resolution images used for validation. We advise extreme care on the validation of candidate planets discovered by space missions. It is important that all the assumptions in the validation process are carefully checked. An independent confirmation is mandatory in order to avoid wasting valuable resources on further characterization of non-existent targets.

OK, they found that 3 out of 104 were really false positives, where only one was expected (statistically), then figured out why so it can be avoided in the future.  Clearly valuable, but it does not change the overall exo-planet statistics much.  If you are trying to do any sort of planetary census, there are much bigger sources of error.  If you are zooming in on one particular star, though, it's worth double checking.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/27/2017 04:15 PM
Posting this mostly because of the seemingly bizarre attitude of the IAU to the naming of this comet, which has resulted in the team who discovered it not being credited.

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Never heard of ASAS-SN? It’s an automated sky survey hunting for supernovae in both hemispheres, with instruments based at Haleakala in Hawaii and Cerro Tololo in Chile. Though the survey targets supernovae, it does on occasion pick up other interesting astronomical phenomena as well. This is the first comet discovery for the ASAS-SN team, as they join the ranks of PanSTARRS, LINEAR and other prolific robotic comet hunters.

Evoking the very name “ASAS-SN” seems to have sparked a minor controversy as well, as the International Astronomical Union (IAU) declined to name the comet after the survey, listing it simply as “C/2017 O1”. Word is, “ASAS-SN” was to close to the word “Assassin” (this is actually controversial?) For our money, we’ll simply keep referring to the comet as “O1 ASAS-SN” as a recognition of the team’s hard work and their terrific discovery.

https://www.universetoday.com/136564/new-comet-c2017-o1-asas-sn-takes-earth-surprise/
Title: Re: Exoplanets And Stars Thread
Post by: hop on 07/27/2017 05:18 PM
OK, they found that 3 out of 104 were really false positives, where only one was expected (statistically), then figured out why so it can be avoided in the future.
It's not clear to me Cabrera et al looked at all 104 of those planets, they were looking at specific planets for followup.
Quote
Clearly valuable, but it does not change the overall exo-planet statistics much.  If you are trying to do any sort of planetary census, there are much bigger sources of error.  If you are zooming in on one particular star, though, it's worth double checking.
It's also important to note that these are K2 planets. K2 data is open to all: Discoveries are made by whoever publishes first and aren't validated by the Kepler team, so this doesn't necessarily have any implication for the main Kepler catalog. My impression is the normal Kepler validation process includes tests that would have flagged these.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/27/2017 05:42 PM
OK, they found that 3 out of 104 were really false positives, where only one was expected (statistically), then figured out why so it can be avoided in the future.
It's not clear to me Cabrera et al looked at all 104 of those planets, they were looking at specific planets for followup.
Quote
Clearly valuable, but it does not change the overall exo-planet statistics much.  If you are trying to do any sort of planetary census, there are much bigger sources of error.  If you are zooming in on one particular star, though, it's worth double checking.
It's also important to note that these are K2 planets. K2 data is open to all: Discoveries are made by whoever publishes first and aren't validated by the Kepler team, so this doesn't necessarily have any implication for the main Kepler catalog. My impression is the normal Kepler validation process includes tests that would have flagged these.

Thanks for clarifying this was for K2, as that makes my posts up thread irrelevant here.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/27/2017 06:50 PM
A Tale of Three Stellar Cities

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Using new observations from ESO’s VLT Survey Telescope, astronomers have discovered three different populations of young stars within the Orion Nebula Cluster. This unexpected discovery adds very valuable new insights for the understanding of how such clusters form. It suggests that star formation might proceed in bursts, where each burst occurs on a much faster time-scale than previously thought.

OmegaCAM — the wide-field optical camera on ESO’s VLT Survey Telescope (VST) — has captured the spectacular Orion Nebula and its associated cluster of young stars in great detail, producing a beautiful new image. This object is one of the closest stellar nurseries for both low and high-mass stars, at a distance of about 1350 light-years [1].

But this is more than just a pretty picture. A team led by ESO astronomer Giacomo Beccari has used these data of unparallelled quality to precisely measure the brightness and colours of all the stars in the Orion Nebula Cluster. These measurements allowed the astronomers to determine the mass and ages of the stars. To their surprise, the data revealed three different sequences of potentially different ages.

“Looking at the data for the first time was one of those ‘Wow!’ moments that happen only once or twice in an astronomer's lifetime,” says Beccari, lead ­author of the paper presenting the results. “The incredible quality of the OmegaCAM images revealed without any doubt that we were seeing three distinct populations of stars in the central parts of Orion.”

Monika Petr-Gotzens, co-author and also based at ESO Garching, continues, “This is an important result. What we are witnessing is that the stars of a cluster at the beginning of their lives didn’t form altogether simultaneously. This may mean that our understanding of how stars form in clusters needs to be modified.”

The astronomers looked carefully at the possibility that instead of indicating different ages, the different brightnesses and colours of some of the stars were due to hidden companion stars, which would make the stars appear brighter and redder than they really were. But this idea would imply quite unusual properties of the pairs, which have never before been observed. Other measurements of the stars, such as their rotation speeds and spectra, also indicated that they must have different ages [2].

“Although we cannot yet formally disprove the possibility that these stars are binaries, it seems much more natural to accept that what we see are three generations of stars that formed in succession, within less than three million years,” concludes Beccari.

The new results strongly suggest that star formation in the Orion Nebula Cluster is proceeding in bursts, and more quickly than had been previously thought.

http://www.eso.org/public/news/eso1723/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/27/2017 08:16 PM
BBC article with additional reporting on the story.

Signal may be from first 'exomoon'

Quote
But Dr Kipping said this is not the best way to gauge the potential detection.
He told BBC News: "We're excited about it... statistically, formally, it's a very high probability. But do we really trust the statistics? That's something unquantifiable. Until we get the measurements from Hubble, it may as well be 50-50 in my mind."
The candidate moon is known as Kepler-1625b I and is observed around a star that lies some 4,000 light-years from Earth. On account of its large size, team members have dubbed it a "Nep-moon".
A current theory of planetary formation suggests such an object is unlikely to have formed in place with its Jupiter-mass planet, but would instead be an object captured by the gravity of the planet later on in the evolution of this planetary system.
The researchers could find no predictions of a Neptune-sized moon in the literature, but Dr Kipping notes that nothing in physics prevents one.
A handful of possible candidates have come to light in the past, but none as yet has been confirmed.
"I'd say it's the best [candidate] we've had," Dr Kipping told me.
"Almost every time we hit a candidate, and it passes our tests, we invent more tests until it finally dies - until it fails one of the tests... in this case we've applied everything we've ever done and it's passed all of those tests. On the other hand, we only have three events."

http://www.bbc.co.uk/news/science-environment-40741545
Title: Re: Exoplanets And Stars Thread
Post by: hop on 07/28/2017 07:31 AM
Here's Alex Teachey and David Kipping (authors of the exomoon paper) talking about the result, and why they ended up going public now

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 07/28/2017 09:53 AM
Good news for James Cameron as if you can get moons the size of Neptune there's nothing to say you couldn't get moons the size of Earth around a super sized gas giant. So you would end up with a system as seen in the film like Avatar if you had more than one of them.
Title: Re: Exoplanets And Stars Thread
Post by: rubtest on 07/28/2017 10:06 AM
Was there any search for tiny moons around the biggest MOONS in the solar systems like Titan , Ganymede ?
I am almost sure it is gravitational an impossibility because of the Jupiter / Saturn strong gravitational fields.
Post by: Star One on 07/28/2017 06:52 PM
New Nature article about the possible exomoon discovery with some useful quotes.

Quote
Jean Schneider, an exomoon hunter at the Paris Observatory, says that the authors were right to make this candidate public. Now, he says, “other people can re-analyse the Kepler data for Kepler-1625 b and make their own opinion”.

Astronomer David Bennett at the University of Notre Dame in Indiana agrees. “I don’t consider it to be terribly controversial to put a paper on the arXiv before it is peer reviewed,” he says. “It is often the case that the journal doesn’t really find the best person to review the paper,” he adds. “If it is posted on arXiv.org, then you might get much more useful comments from a real expert who wasn’t picked by the journal to review the paper.”

http://www.nature.com/news/why-astronomers-reluctantly-announced-a-possible-exomoon-discovery-1.22377
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/01/2017 02:36 AM
Four new short-period giant planets discovered (https://phys.org/news/2017-07-short-period-giant-planets.html)

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Astronomers have detected four new giant exoplanets as part of the Hungarian-made Automated Telescope Network-South (HATSouth) exoplanet survey. The newly found alien worlds are about the size of Jupiter, but less massive. They transit moderately bright stars and have short orbital periods.

Quote
According to the paper, HATS-45b is the largest and most massive exoworld of all the newly discovered exoplanets. It has a radius of about 1.29 Jupiter radii and is 30 percent less massive than our solar system's biggest planet. It orbits its parent star every 4.19 days.

HATS-46b has the longest orbital period and is the least massive of the newly found quartet. It has only 17 percent of the mass of Jupiter, however a radius of approximately 0.9 Jupiter radii. It takes this planet 4.74 days to fully circle its host.

HATS-43b and HATS-44b are similar in radius—1.18 and 1.07 Jupiter radii respectively. HATS-43b has a mass of 0.26 Jupiter masses, while HATS-44b is about two times more massive—0.56 Jupiter masses. The shortest orbital period among the four newly identified planets belongs to HATS-44b, which orbits its star in just 2.74 days. When it comes to HATS-43b, it takes it approximately 4.39 days to circle its parent star.
Title: Re: Exoplanets And Stars Thread
Post by: Phil Stooke on 08/01/2017 02:57 AM
"Was there any search for tiny moons around the biggest MOONS in the solar systems like Titan , Ganymede ?"

I can't give a source at the moment, but I believe there have been searches for rings and moons around the larger moons of Saturn, at least.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/01/2017 04:40 PM

Exomoons: Rare in Inner Stellar Systems?

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With all this in mind, every paper that comes out of HEK gets my attention. Kipping (Columbia University), working with graduate student Alex Teachey and citizen scientist Allan Schmitt, has now produced a paper that takes a significant step as the investigation proceeds. We have no detection yet — more about that in a moment — but we do have a broader result showing that exomoons are unusual in the inner regions of the systems surveyed.

Kipping and Teachey looked at 284 viable moon-hosting Kepler planetary candidates to search for moons around planets from Earth to Jupiter in size and distances from their stars of 0.1 to 1 AU. This finding seems to be getting less attention in the press than it deserves, so let’s dig into the paper on it:

Our results place new upper limits on the exomoon population for planets orbiting within about 1 AU of their host star, upper limits that are remarkably low. We have also analyzed subsets of the ensemble to test the effect of various data cuts, and we have identified the regime in which the OSE model presented in Heller (2014) breaks down, which we call the “Callisto Effect” — beyond 20 planetary radii, discrepancies appear in the results.

Quote
Back to the paper:

Our analysis suggests that exomoons may be quite rare around planets at small semi-major axes, a finding that supports theoretical work suggesting moons may be lost as planets migrate inward. On the other hand, if the dearth of exomoons can be read as a reliable indicator of migration, our results suggest a large fraction of the planets in the ensemble have migrated to their present location.

And that is a pointer to which we need to pay attention. Is a lack of exomoons a marker for planetary migration? If further analysis determines that it is, then we’ve found an extremely handy tool for studying the formation history of other stellar systems

https://www.centauri-dreams.org/?p=38214
Post by: Star One on 08/03/2017 08:32 AM
Hubble detects exoplanet with glowing water atmosphere

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Scientists have discovered the strongest evidence to date for a stratosphere on a planet outside our solar system, or exoplanet. A stratosphere is a layer of atmosphere in which temperature increases with higher altitudes.

“This result is exciting because it shows that a common trait of most of the atmospheres in our solar system — a warm stratosphere — also can be found in exoplanet atmospheres,” said Mark Marley, study co-author based at NASA’s Ames Research Center in California’s Silicon Valley. “We can now compare processes in exoplanet atmospheres with the same processes that happen under different sets of conditions in our own solar system.”

Reporting in the journal Nature, scientists used data from NASA’s Hubble Space Telescope to study WASP-121b, a type of exoplanet called a “hot Jupiter.” Its mass is 1.2 times that of Jupiter, and its radius is about 1.9 times Jupiter’s — making it puffier. But while Jupiter revolves around our sun once every 12 years, WASP-121b has an orbital period of just 1.3 days. This exoplanet is so close to its star that if it got any closer, the star’s gravity would start ripping it apart. It also means that the top of the planet’s atmosphere is heated to a blazing 4,600 degrees Fahrenheit (2,500 degrees Celsius), hot enough to boil some metals. The WASP-121 system is estimated to be about 900 light-years from Earth — a long way, but close by galactic standards.

https://astronomynow.com/2017/08/02/hubble-detects-exoplanet-with-glowing-water-atmosphere/

Astronomers discover ‘heavy metal’ supernova rocking out

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Following the recent discovery of one of these “superluminous supernovas”, a team of astronomers led by Matt Nicholl from the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., has uncovered vital clues about where some of these extraordinary objects come from.

Cambridge University’s Gaia Science Alerts team discovered this supernova, dubbed SN 2017egm, on May 23, 2017 with the European Space Agency’s Gaia satellite. A team led by Subo Dong of the Kavli Institute for Astronomy and Astrophysics at Peking University used the Nordic Optical Telescope to identify it as a superluminous supernova.

SN 2017egm is located in a spiral galaxy about 420 million light years from Earth, making it about three times closer than any other superluminous supernova previously seen. Dong realized that the galaxy was very surprising, as virtually all known superluminous supernovas have been found in dwarf galaxies that are much smaller than spiral galaxies like the Milky Way.

Building on this discovery, the CfA team found that SN 2017egm’s host galaxy has a high concentration of elements heavier than hydrogen and helium, which astronomers call “metals”. This is the first clear evidence for a metal-rich birthplace for a superluminous supernova. The dwarf galaxies that usually host superluminous supernovas are known to have a low metal content, which was thought to be an essential ingredient for making these explosions.

“Superluminous supernovas were already the rock stars of the supernova world,” said Nicholl. “We now know that some of them like heavy metal, so to speak, and explode in galaxies like our own Milky Way.”

https://astronomynow.com/2017/08/02/astronomers-discover-heavy-metal-supernova-rocking-out/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/03/2017 07:33 PM
Disintegrating Rocky Exoplanets

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We discuss a new class of exoplanets that appear to be emitting a tail of dusty effluents. These disintegrating planets are found close to their host stars and have very hot, and likely molten, surfaces. The properties of the dust should provide a direct probe of the constituent material of these rocky bodies.

https://arxiv.org/abs/1708.00633
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/03/2017 07:53 PM
Gravity Waves Detected In Sun's Interior Reveal Rapidly Rotating Core

Quote
Scientists using the ESA/NASA SOHO solar observatory have found long-sought gravity modes of seismic vibration that imply the Sun’s core is rotating four times faster than its surface.

http://m.esa.int/Our_Activities/Space_Science/Space_Science/Gravity_waves_detected_in_Sun_s_interior_reveal_rapidly_rotating_core
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/04/2017 08:10 PM
Bad News For Proxima b: An Earth-Like Atmosphere Might Not Survive There

Quote
So it’s not all bad news, but it doesn’t inspire a lot of confidence either. Unless Proxima b is a volcanically-active planet and subject to a lot of cometary impacts, it is not likely be temperate, water-bearing world. Most likely, its climate will be analogous to Mars – cold, dry, and with water existing mostly in the form of ice. And as for indigenous life emerging there, that’s not too likely either.

These and other recent studies have painted a rather bleak picture about the habitability of red dwarf star systems. Given that these are the most common types of stars in the known Universe, the statistical likelihood of finding a habitable planet beyond our Solar System appears to be dropping. Not exactly good news at all for those hoping that life will be found out there within their lifetimes!

But it is important to remember that what we can say definitely at this point about extra-solar planets is limited. In the coming years and decades, next-generation missions – like the James Webb Space Telescope (JWST) and the Transiting Exoplanet Survey Satellite (TESS) –  are sure to paint a more detailed picture. In the meantime, there’s still plenty of stars in the Universe, even if most of them are extremely far away!

Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/09/2017 02:56 PM
Four Earth-sized planets detected orbiting the nearest sun-like star (https://news.ucsc.edu/2017/08/tau-ceti-planets.html)

(http://i.imgur.com/Lyin3Sf.jpg)

(http://i.imgur.com/hIXxlWJ.png)

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A new study by an international team of astronomers reveals that four Earth-sized planets orbit the nearest sun-like star, tau Ceti, which is about 12 light years away and visible to the naked eye. These planets have masses as low as 1.7 Earth mass, making them among the smallest planets ever detected around nearby sun-like stars. Two of them are super-Earths located in the habitable zone of the star, meaning they could support liquid surface water.

The planets were detected by observing the wobbles in the movement of tau Ceti. This required techniques sensitive enough to detect variations in the movement of the star as small as 30 centimeters per second.

"We are now finally crossing a threshold where, through very sophisticated modeling of large combined data sets from multiple independent observers, we can disentangle the noise due to stellar surface activity from the very tiny signals generated by the gravitational tugs from Earth-sized orbiting planets," said coauthor Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz.

According to lead author Fabo Feng of the University of Hertfordshire, UK, the researchers are getting tantalizingly close to the 10-centimeter-per-second limit required for detecting Earth analogs. "Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth's habitability through comparison with these analogs," Feng said. "We have introduced new methods to remove the noise in the data in order to reveal the weak planetary signals."

The outer two planets around tau Ceti are likely to be candidate habitable worlds, although a massive debris disc around the star probably reduces their habitability due to intensive bombardment by asteroids and comets.

The same team also investigated tau Ceti four years ago in 2013, when coauthor Mikko Tuomi of the University of Hertfordshire led an effort in developing data analysis techniques and using the star as a benchmark case. "We came up with an ingenious way of telling the difference between signals caused by planets and those caused by star's activity. We realized that we could see how star's activity differed at different wavelengths and use that information to separate this activity from signals of planets," Tuomi said.

The researchers painstakingly improved the sensitivity of their techniques and were able to rule out two of the signals the team had identified in 2013 as planets. "But no matter how we look at the star, there seem to be at least four rocky planets orbiting it," Tuomi said. "We are slowly learning to tell the difference between wobbles caused by planets and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable planets in the system."

Color difference makes a difference: four planet candidates around tau Ceti (https://arxiv.org/abs/1708.02051)

If confirmed, there would seem to be decent room for an Earth mass planet in the middle of the habitable zone which wouldn't currently be detectable.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/09/2017 06:49 PM
Is Tau Ceti more sunlike than either of the Alpha Centauri stars then?
Title: Re: Exoplanets And Stars Thread
Post by: Bob Shaw on 08/09/2017 07:12 PM
Have any planets been *really* detected around Bernard's Star? It would be rather nice!
Title: Re: Exoplanets And Stars Thread
Post by: zubenelgenubi on 08/09/2017 07:37 PM
Re: nearest sun-like star

Star                      Mass, in solar masses   Spectral Type (Sun = G2V)

Alpha Centauri A    1.10                           G2V

Alpha Centauri B    0.91                            K1V

Sirius A                 2.02                            A1V

Epsilon Eridani       0.82                            K2V

Procyon A             1.50                            F5V-IV

Epsilon Indi A        0.76                             K5V

Tau Ceti                0.78                            G8V

They may be applying data in a partly-subjective manner to claim "nearest sun-like star:"
distance, Main Sequence star near 1 solar mass, not part of a binary or multiple star system, etc.
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 08/09/2017 07:38 PM
It is noteworthy that if the planetary system is aligned with the debris disk (which seems very likely), the true masses of the four planets are about double their minimum masses. So the inner two planets would be large super-Earths, whereas the outer two would be mini-Neptunes.

@StarOne: I think of these three stars, Alpha Cen A is most sun-like. It is also a G2V type, is only 10% more massive and has a similar rotation period. Then Tau Ceti, then Alpha Cen B.

@Bob Shaw: the planets that van de Kamp thought were there (in the 1960ies) do not exist, this we know for sure. Otherwise, we only have upper limits on mass/distance (<7.5 Earth masses in the habitable zone, e.g.). The Red Dots (https://twitter.com/RedDotsSpace) project is bound to find out!
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/09/2017 08:23 PM
It is noteworthy that if the planetary system is aligned with the debris disk (which seems very likely), the true masses of the four planets are about double their minimum masses. So the inner two planets would be large super-Earths, whereas the outer two would be mini-Neptunes.

@StarOne: I think of these three stars, Alpha Cen A is most sun-like. It is also a G2V type, is only 10% more massive and has a similar rotation period. Then Tau Ceti, then Alpha Cen B.

@Bob Shaw: the planets that van de Kamp thought were there (in the 1960ies) do not exist, this we know for sure. Otherwise, we only have upper limits on mass/distance (<7.5 Earth masses in the habitable zone, e.g.). The Red Dots (https://twitter.com/RedDotsSpace) project is bound to find out!

Thank you. Could you direct me towards any articles or papers speculating on the origins of the debris disk around Tau Ceti?
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 08/09/2017 08:34 PM
It is noteworthy that if the planetary system is aligned with the debris disk (which seems very likely), the true masses of the four planets are about double their minimum masses. So the inner two planets would be large super-Earths, whereas the outer two would be mini-Neptunes.

@StarOne: I think of these three stars, Alpha Cen A is most sun-like. It is also a G2V type, is only 10% more massive and has a similar rotation period. Then Tau Ceti, then Alpha Cen B.

@Bob Shaw: the planets that van de Kamp thought were there (in the 1960ies) do not exist, this we know for sure. Otherwise, we only have upper limits on mass/distance (<7.5 Earth masses in the habitable zone, e.g.). The Red Dots (https://twitter.com/RedDotsSpace) project is bound to find out!

Thank you. Could you direct me towards any articles or papers speculating on the origins of the debris disk around Tau Ceti?

Look here for a recent overview of the situation (although still with the originally proposed 5 planets):

The classic paper on the Tau Ceti debris disk is probably this one: http://adsabs.harvard.edu/abs/2004MNRAS.351L..54G
Post by: Star One on 08/09/2017 08:38 PM
It is noteworthy that if the planetary system is aligned with the debris disk (which seems very likely), the true masses of the four planets are about double their minimum masses. So the inner two planets would be large super-Earths, whereas the outer two would be mini-Neptunes.

@StarOne: I think of these three stars, Alpha Cen A is most sun-like. It is also a G2V type, is only 10% more massive and has a similar rotation period. Then Tau Ceti, then Alpha Cen B.

@Bob Shaw: the planets that van de Kamp thought were there (in the 1960ies) do not exist, this we know for sure. Otherwise, we only have upper limits on mass/distance (<7.5 Earth masses in the habitable zone, e.g.). The Red Dots (https://twitter.com/RedDotsSpace) project is bound to find out!

Thank you. Could you direct me towards any articles or papers speculating on the origins of the debris disk around Tau Ceti?

Look here for a recent overview of the situation (although still with the originally proposed 5 planets):

The classic paper on the Tau Ceti debris disk is probably this one: http://adsabs.harvard.edu/abs/2004MNRAS.351L..54G

Thanks that second paper sounds interesting.

Seems likely any life that might have got going would probably have been 'bombed' out of existence by that debris disk.
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/09/2017 08:55 PM
It's only necessary for unicellular photosynthetic organisms to survive long enough that there's enough oxygen in the atmosphere to detect. I'm not convinced that oceans full of unicellular life would be completely wiped out by asteroid and comet impacts.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/09/2017 09:03 PM
It's only necessary for unicellular photosynthetic organisms to survive long enough that there's enough oxygen in the atmosphere to detect. I'm not convinced that oceans full of unicellular life would be completely wiped out by asteroid and comet impacts.

But with that kind of disc isn't there a danger that the bombardment would be so heavy that it would leave the surfaces of these planets something like IO.
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/09/2017 09:18 PM
It's "only" estimated to be 10x the frequency as on Earth, which might be an issue for complex life, but shouldn't be an issue for unicellular life. I would also guess that super Earths are more likely to have denser atmospheres than Earth, which would help to mitigate the higher frequency of impacts to an extent.

Cometary impacts might also be beneficial for life, bringing water and organics.

Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 08/09/2017 09:42 PM
Note that its just that the mass of the debris disk is estimated to be about 10x the mass of the Kuiper belt. To go from there to a 10x higher bombardment rate on the planets in the system is quite problematic. After all, the Earth is primarily bombarded from the asteroid belt, not the Kuiper belt! Bombardment rates on planets primarily depend on the efficiency of delivery of small bodies to planet-crossing orbits (e.g. through resonances and non-gravitational forces), which in turn depends on the system planetary architecture. We know nothing of planets in the outer part (>1 AU) of the Tau Ceti system. Without a detailed simulation, talk of relative bombardment rates and its implications for life on these planets is pure fantasy.
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/09/2017 10:34 PM
Good point, but I still think it's reasonable to assume a higher frequency of impacts. Still, even if that does have an impact on complex life, it's still possible that unicellular photosynthetic life could recover quickly and it might be possible to detect evidence of (or indeed lack of) oxygen in exoplanet atmospheres in the future.

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/10/2017 07:27 PM
Hint of relativity effects in stars orbiting centre of galaxy

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A new analysis of data from ESO’s Very Large Telescope and other telescopes suggests that the orbits of stars around the supermassive black hole at the centre of the Milky Way may show the subtle effects predicted by Einstein’s general theory of relativity. There are hints that the orbit of the star S2 is deviating slightly from the path calculated using classical physics. This tantalising result is a prelude to much more precise measurements and tests of relativity that will be made using the GRAVITY instrument as star S2 passes very close to the black hole in 2018.

https://astronomynow.com/2017/08/10/hint-of-relativity-effects-in-stars-orbiting-centre-of-galaxy/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/11/2017 09:24 PM
Two bright, variable sources with unusual light curves discovered by ASAS-SN

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As part of an ongoing effort by ASAS-SN project (Shappee et al. 2014; Kochanek et al. 2017) to characterize and catalog all bright variable stars, we have discovered two bright, variable sources with unusual light curves---ASASSN-V J033455.88-053957.9 (mean V~13.0) and ASASSN-V J211014.40-242105.3 (mean V~14.5).

ASASSN-V J033455.88-053957.9 raises slowly in brightness by ~0.5 mag in ~1,800 days (ASAS-SN Sky Patrol light curve; data points in red are likely affected by artifacts and should not be taken into consideration). A spectrum of this source was obtained by the RAVE survey (Kunder et al. 2017) giving values of T_eff=3660 K and log g =5.1 cm/s^2, fairly typical for an early-type M-dwarf. The 2MASS colors for this source (J-H=0.59 and H-Ks=0.10) also correspond to M1/M2 spectral type M-dwarf (West et al. 2011). ASASSN-V J033455.88-053957.9 appears in a number of X-ray catalogs, including the Swift X-ray point source catalogue (Evans et al. 2014). ASAS-SN light curve for ASASSN-V J033455.88-053957.9 is very unusual for an M-dwarf, and we encourage further observations of this source.

ASASSN-V J211014.40-242105.3 (ASAS-SN Sky Patrol light curve) is mostly flat at around V~14.5 mag, with a big drop in brightness of at least ~2 mag, lasting at least 150 days. This source was spectroscopically classified as a cataclysmic variable, with Balmer and HeII 4686A emission lines (Kilkenny et al. 2015). We conclude that ASASSN-V J211014.40-242105.3 is most likely a cataclysmic variable (CV) of the VY Scl type.

We thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Chinese Academy of Sciences South America Center for Astronomy (CASSACA).

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/12/2017 07:45 PM
TRAPPIST-1 is Older Than Our Solar System

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If we want to know more about whether life could survive on a planet outside our solar system, it's important to know the age of its star. Young stars have frequent releases of high-energy radiation called flares that can zap their planets' surfaces. If the planets are newly formed, their orbits may also be unstable. On the other hand, planets orbiting older stars have survived the spate of youthful flares, but have also been exposed to the ravages of stellar radiation for a longer period of time.

Scientists now have a good estimate for the age of one of the most intriguing planetary systems discovered to date -- TRAPPIST-1, a system of seven Earth-size worlds orbiting an ultra-cool dwarf star about 40 light-years away. Researchers say in a new study that the TRAPPIST-1 star is quite old: between 5.4 and 9.8 billion years. This is up to twice as old as our own solar system, which formed some 4.5 billion years ago.

The seven wonders of TRAPPIST-1 were revealed earlier this year in a NASA news conference, using a combination of results from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, NASA's Spitzer Space Telescope, and other ground-based telescopes. Three of the TRAPPIST-1 planets reside in the star's "habitable zone," the orbital distance where a rocky planet with an atmosphere could have liquid water on its surface. All seven planets are likely tidally locked to their star, each with a perpetual dayside and nightside.

At the time of its discovery, scientists believed the TRAPPIST-1 system had to be at least 500 million years old, since it takes stars of TRAPPIST-1's low mass (roughly 8 percent that of the Sun) roughly that long to contract to its minimum size, just a bit larger than the planet Jupiter. However, even this lower age limit was uncertain; in theory, the star could be almost as old as the universe itself. Are the orbits of this compact system of planets stable? Might life have enough time to evolve on any of these worlds?

"Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago," said Adam Burgasser, an astronomer at the University of California, San Diego, and the paper's first author. Burgasser teamed up with Eric Mamajek, deputy program scientist for NASA's Exoplanet Exploration Program based at NASA's Jet Propulsion Laboratory, Pasadena, California, to calculate TRAPPIST-1's age. Their results will be published in The Astrophysical Journal.

It is unclear what this older age means for the planets' habitability. On the one hand, older stars flare less than younger stars, and Burgasser and Mamajek confirmed that TRAPPIST-1 is relatively quiet compared to other ultra-cool dwarf stars. On the other hand, since the planets are so close to the star, they have soaked up billions of years of high-energy radiation, which could have boiled off atmospheres and large amounts of water. In fact, the equivalent of an Earth ocean may have evaporated from each TRAPPIST-1 planet except for the two most distant from the host star: planets g and h. In our own solar system, Mars is an example of a planet that likely had liquid water on its surface in the past, but lost most of its water and atmosphere to the Sun's high-energy radiation over billions of years.

However, old age does not necessarily mean that a planet's atmosphere has been eroded. Given that the TRAPPIST-1 planets have lower densities than Earth, it is possible that large reservoirs of volatile molecules such as water could produce thick atmospheres that would shield the planetary surfaces from harmful radiation. A thick atmosphere could also help redistribute heat to the dark sides of these tidally locked planets, increasing habitable real estate. But this could also backfire in a "runaway greenhouse" process, in which the atmosphere becomes so thick the planet surface overheats - as on Venus.

"If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years," Burgasser said.

Fortunately, low-mass stars like TRAPPIST-1 have temperatures and brightnesses that remain relatively constant over trillions of years, punctuated by occasional magnetic flaring events. The lifetimes of tiny stars like TRAPPIST-1 are predicted to be much, much longer than the 13.7 billion-year age of the universe (the Sun, by comparison, has an expected lifetime of about 10 billion years).

"Stars much more massive than the Sun consume their fuel quickly, brightening over millions of years and exploding as supernovae," Mamajek said. "But TRAPPIST-1 is like a slow-burning candle that will shine for about 900 times longer than the current age of the universe."

Some of the clues Burgasser and Mamajek used to measure the age of TRAPPIST-1 included how fast the star is moving in its orbit around the Milky Way (speedier stars tend to be older), its atmosphere's chemical composition, and how many flares TRAPPIST-1 had during observational periods. These variables all pointed to a star that is substantially older than our Sun.

Future observations with NASA's Hubble Space Telescope and upcoming James Webb Space Telescope may reveal whether these planets have atmospheres, and whether such atmospheres are like Earth's.

"These new results provide useful context for future observations of the TRAPPIST-1 planets, which could give us great insight into how planetary atmospheres form and evolve, and persist or not," said Tiffany Kataria, exoplanet scientist at JPL, who was not involved in the study.

Future observations with Spitzer could help scientists sharpen their estimates of the TRAPPIST-1 planets' densities, which would inform their understanding of their compositions.

https://exoplanets.nasa.gov/trappist1
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/12/2017 07:53 PM
Here's the relevant paper.

On the Age of the TRAPPIST-1 System

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The nearby (d = 12 pc) M8 dwarf star TRAPPIST-1 (2MASS J23062928-0502285) hosts a compact system of at least seven exoplanets with sizes similar to Earth. Given its importance for testing planet formation and evolution theories, and for assessing the prospects for habitability among Earth-size exoplanets orbiting the most common type of star in the Galaxy, we present a comprehensive assessment of the age of this system. We collate empirical age constraints based on the color-absolute magnitude diagram, average density, lithium absorption, surface gravity features, metallicity, kinematics, rotation, and magnetic activity; and conclude that TRAPPIST-1 is a transitional thin/thick disk star with an age of 7.6±2.2 Gyr. The star's color-magnitude position is consistent with it being slightly metal-rich ([Fe/H] ≃ +0.06), in line with its previously reported near-infrared spectroscopic metallicity; and it has a radius (R = 0.121±0.003 R⊙) that is larger by 8-14% compared to solar-metallicity evolutionary models. We discuss some implications of the old age of this system with regard to the stability and habitability of its planets.

https://arxiv.org/abs/1706.02018
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 08/14/2017 06:34 AM
A planetary system around near-by YZ Ceti.

https://arxiv.org/abs/1708.03336

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The HARPS search for southern extra-solar planets XLII. A system of Earth-mass planets around the nearby M dwarf YZ Cet

Exoplanet surveys have shown that systems with multiple low-mass planets on compact orbits are common. Except for few cases, however, the masses of these planets are generally unknown. At the very end of the main sequence, host stars have the lowest mass and hence offer the largest reflect motion for a given planet. In that context, we monitored the low-mass (0.13Msun) M dwarf YZ Cet (GJ 54.1, HIP 5643) intensively and obtained both radial velocities and stellar-activity indicators derived from both spectroscopy and photometry. We find strong evidence that it is orbited by at least three planets in compact orbits (P=1.97, 3.06, 4.66 days), with the inner two near a 2:3 mean-motion resonance. The minimum masses are comparable to that of Earth (Msini=0.75+-0.13, 0.98+-0.14, and 1.14+-0.17 Mearth) and also the lowest masses measured by radial velocity so far. We note the possibility for an even lower-mass, fourth planet with Msini=0.472+-0.096 Mearth at P=1.04 days. An n-body dynamical model is used to put further constraints on the system parameters. At 3.6 parsecs, YZ Cet is the nearest multi-planet system detected to date.

Cool factoid: YZ Ceti is a star currently located only 1.6 LY from Tau Ceti.
Post by: Star One on 08/15/2017 07:32 PM
Tidally locked exoplanets may be more common than previously thought

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Many exoplanets to be found by coming high-powered telescopes will probably be tidally locked — with one side permanently facing their host star — according to new research by astronomer Rory Barnes of the University of Washington.

Barnes, a UW assistant professor of astronomy and astrobiology, arrived at the finding by questioning the long-held assumption that only those stars that are much smaller and dimmer than the sun could host orbiting planets that were in synchronous orbit, or tidally locked, as the moon is with the Earth. His paper, “Tidal Locking of Habitable Exoplanets,” has been accepted for publication by the journal Celestial Mechanics and Dynamical Astronomy.

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Barnes writes: “These results suggest that the process of tidal locking is a major factor in the evolution of most of the potentially habitable exoplanets to be discovered in the near future.”

Being tidally locked was once thought to lead to such extremes of climate as to eliminate any possibility of life, but astronomers have since reasoned that the presence of an atmosphere with winds blowing across a planet’s surface could mitigate these effects and allow for moderate climates and life.

Barnes said he also considered the planets that will likely be discovered by NASA’s next planet-hunting satellite, the Transiting Exoplanet Survey Satellite or TESS, and found that every potentially habitable planet it will detect will likely be tidally locked.

http://www.washington.edu/news/2017/08/14/tidally-locked-exoplanets-may-be-more-common-than-previously-thought/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/16/2017 08:00 PM
Tuning Up RV: A Test Case at Tau Ceti

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And so on. The lesson is clear enough: We have to be extremely careful when interpreting signals below 1 meter per second, the range in which we’ll need to identify Earth-class planets.

But the value of radial velocity is unquestioned. Unlike the transit technique, we don’t have to rely on a fortuitous line-up between a distant planetary system and the Earth — we can therefore extend it to all bright stars of interest. Feng and colleagues think we will be able to use new high precision spectrometers along with these emerging statistical and noise models to find a true Earth analog in the coming decade. Thus this work on Tau Ceti, modeling wavelength-dependent noise, becomes a test case of a new noise model framework that can help us filter background noise out of RV observations.

https://www.centauri-dreams.org/?p=38293
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/17/2017 03:07 PM
We may have caught supernova debris slamming into neighboring stars

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In a new paper, a large team of researchers notes that a couple of recent supernovae have shown an unexpected excess of blue light. They then go on to describe the supernova SN 2017cbv, which became visible in March of this year. In this case, the supernova was spotted only a day after the explosion took place. Follow-up observations over the next six weeks allowed the team to build up a detailed record of the aftermath of the supernova (called a light curve). This record was then compared to what we'd expect from a typical type-Ia supernova.

Compared to a standard type-Ia supernova, SN 2017cbv showed an excess of light at all wavelengths, including the blue and UV regions. This was mostly pronounced during the first week after the explosion, as the light ramped up toward its peak. At the peak, there was an excess in redder wavelengths than you'd see in a typical type-Ia supernova.

What could cause this? To find out, the team modified a model of type-Ia supernovae to include a shockwave running into a nearby star. The modified model fits the data well and suggests that somewhere between five and 15 percent of the light during the peak came from the shockwave hitting a nearby star.

The model, however, suggests that the companion star was nearly 40 million miles from the white dwarf (which is a bit closer than Mercury is to our Sun). That's right on the far edge of where you'd expect the companion star to be if the two were close enough to share material. However, the authors point out that this model assumes that they're looking at the event-companion with an ideal viewing angle. If the angle is off, it would look dimmer, which would make the companion star appear to be farther away.

https://arstechnica.com/science/2017/08/we-may-have-caught-supernova-debris-slamming-into-neighboring-stars/
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 08/18/2017 02:15 AM
One of the commenters identified the paper on arXiv: Early Blue Excess from the Type Ia Supernova 2017cbv and Implications for Its Progenitor (https://arxiv.org/abs/1706.08990).

Unfortunately, they don't say what happened to the companion star. :(
Title: Re: Exoplanets And Stars Thread
Post by: NIVbV-O77OdV-VSVN-Op-SLE7 on 08/18/2017 03:33 AM
How is it determined if an exoplanet is really orbiting a star?  In other words, there could be some some lost asteroid sized object millions of light years in between us and the star.  Maybe there is an Oort Cloud object eclipsing a star?  It would just periodically move in front of a star to dim the light

Just imagine a boat bobbing on water while watching something on the horizon reappear/disappear.

Title: Re: Exoplanets And Stars Thread
Post by: Kesarion on 08/18/2017 08:13 AM
How is it determined if an exoplanet is really orbiting a star?  In other words, there could be some some lost asteroid sized object millions of light years in between us and the star.  Maybe there is an Oort Cloud object eclipsing a star?  It would just periodically move in front of a star to dim the light

As far as I can remember, in order for a Kepler candidate to be confirmed as an exoplanet, they must observe 3 periodic eclipses and also be confirmed by a ground based telescope. That might have changed since 2013 though.
Title: Re: Exoplanets And Stars Thread
Post by: gospacex on 08/18/2017 08:36 AM
How is it determined if an exoplanet is really orbiting a star?  In other words, there could be some some lost asteroid sized object millions of light years in between us and the star.

Asteroid-sized object would not be detectable - the dip is too small.

Quote
Maybe there is an Oort Cloud object eclipsing a star?  It would just periodically move in front of a star to dim the light

In this case, "periodically" would mean "every 500k years".
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/18/2017 06:35 PM
Dynamics of a Probable Earth-mass Planet in the GJ 832 System

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The stability of planetary orbits around the GJ 832 star system, which contains inner (GJ 832c) and outer (GJ 832b) planets, is investigated numerically and a detailed phase-space analysis is performed. Special attention is given to the existence of stable orbits for a planet less than 15 M ⊕ that is injected between the inner and outer planets. Thus, numerical simulations are performed for three and four bodies in elliptical orbits (or circular for special cases) by using a large number of initial conditions that cover the selected phase-spaces of the planet's orbital parameters. The results presented in the phase-space maps for GJ 832c indicate the least deviation of eccentricity from its nominal value, which is then used to determine its inclination regime relative to the star–outer planet plane. Also, the injected planet is found to display stable orbital configurations for at least one billion years. Then, the radial velocity curves based on the signature from the Keplerian motion are generated for the injected planets with masses 1 M ⊕ to 15 M ⊕ in order to estimate their semimajor axes and mass limits. The synthetic RV signal suggests that an additional planet of mass ≤15 M ⊕ with a dynamically stable configuration may be residing between 0.25 and 2.0 au from the star. We have provided an estimated number of RV observations for the additional planet that is required for further observational verification.

http://iopscience.iop.org/article/10.3847/1538-4357/aa80e2/meta
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/18/2017 07:04 PM
Habitable Planet Reality Check: Tau Ceti

http://www.drewexmachina.com/2017/08/18/habitable-planet-reality-check-tau-ceti/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/18/2017 07:23 PM
Scientists improve brown dwarf weather forecasts

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To make sense of the ups and downs of brightness, scientists had to rethink their assumptions about what was going on in the brown dwarf atmospheres. The best model to explain the variations involves large waves, propagating through the atmosphere with different periods. These waves would make the cloud structures rotate with different speeds in different bands.

University of Arizona researcher Theodora Karalidi used a supercomputer and a new computer algorithm to create maps of how clouds travel on these brown dwarfs.

“When the peaks of the two waves are offset, over the course of the day there are two points of maximum brightness,” Karalidi said. “When the waves are in sync, you get one large peak, making the brown dwarf twice as bright as with a single wave.”

The results explain the puzzling behavior and brightness changes that researchers previously saw. The next step is to try to better understand what causes the waves that drive cloud behavior.

https://astronomynow.com/2017/08/17/scientists-improve-brown-dwarf-weather-forecasts/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/18/2017 09:50 PM
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 08/18/2017 11:16 PM
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/18/2017 11:19 PM
Only in as far as most stars are believed to have planets. Most of the nearest stars (https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs) to 16.3 ly* still don't even have candidate planets yet.

*To 21 ly (http://www.johnstonsarchive.net/astro/nearstar.html), as Wikipedia doesn't seem to have a list of stars (https://en.wikipedia.org/wiki/Category:Lists_of_stars) from 16.3 - 20 ly.
Title: Re: Exoplanets And Stars Thread
Post by: redliox on 08/19/2017 05:30 AM
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Only in as far as most stars are believed to have planets. Most of the nearest stars (https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs) to 16.3 ly* still don't even have candidate planets yet.

*To 21 ly (http://www.johnstonsarchive.net/astro/nearstar.html), as Wikipedia doesn't seem to have a list of stars (https://en.wikipedia.org/wiki/Category:Lists_of_stars) from 16.3 - 20 ly.

Although fortunately we have TESS and the JWST coming up, I'd like to see an effort to catalog specifically our neighboring stars.  I don't expect it to be easy, but it would be worth it.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/19/2017 08:14 AM
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)

Aren't Pale Red Dot now studying all our local red dwarfs for planets?
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/19/2017 11:38 AM
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Only in as far as most stars are believed to have planets. Most of the nearest stars (https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs) to 16.3 ly* still don't even have candidate planets yet.

*To 21 ly (http://www.johnstonsarchive.net/astro/nearstar.html), as Wikipedia doesn't seem to have a list of stars (https://en.wikipedia.org/wiki/Category:Lists_of_stars) from 16.3 - 20 ly.

Although fortunately we have TESS and the JWST coming up, I'd like to see an effort to catalog specifically our neighboring stars.  I don't expect it to be easy, but it would be worth it.

ESPRESSO (https://www.eso.org/public/teles-instr/paranal-observatory/vlt/vlt-instr/espresso/) should also be helpful with that. It's an order of magnitude more sensitive than HARPS and should be online this year (if not already, it saw first light nearly a year ago).
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/19/2017 02:24 PM
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)

Aren't Pale Red Dot now studying all our local red dwarfs for planets?

AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/19/2017 02:25 PM
Does this mean now that with the exception of Alpha Centauri all the stars near to Sol are believed to have planets?
Proxima Centauri (and its planet) is the 'C' component of the Alpha Centauri system. However, neither Alpha Centauri A or B are known to have planets. Nor does Barnard's Star (4th nearest), Wolf 359 (5th), Sirius (6th), Gliese 65 A and B (7th and 8th), Ross 154 (9th) and Ross 248 (10th)!

(Disregarding brown and white dwarfs - though none of those closer than Ross 248 are known to have planets either.)

Aren't Pale Red Dot now studying all our local red dwarfs for planets?

AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.

Out of interest what was the criteria for choosing those three out of all the red dwarfs near Sol?
Title: Re: Exoplanets And Stars Thread
Post by: Alpha_Centauri on 08/19/2017 02:42 PM
Because they are visible from La Silla at this time of year and are bright enough for high-res spectroscopy.
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 08/19/2017 03:21 PM
There is a candidate for a Super Earth (https://arxiv.org/abs/1702.03571) around Lalande 21185, the 6th closest main sequence star / 4th closest star system (it's missing from CuddlyRocket's list).
Title: Re: Exoplanets And Stars Thread
Post by: Hungry4info3 on 08/19/2017 05:33 PM
Aren't Pale Red Dot now studying all our local red dwarfs for planets?
AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.
Out of interest what was the criteria for choosing those three out of all the red dwarfs near Sol?
Because they are visible from La Silla at this time of year and are bright enough for high-res spectroscopy.
To add to that, there has been a shift in in strategy in recent years for radial velocity surveys away from "Sample numerous stars a few times each" to "Sample a few stars numerous times each." The first one easily catches your intermediate- and long-period giant planets, but to get down to low-mass planets, you have to really drill a star to get enough data to overcome statistical noise. Detecting low-mass planets in the solar neighborhood is now finally feasible, so rather than observing all the local M dwarfs in the sky, we're focusing on hitting a few nearby, bright systems.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/19/2017 05:45 PM
Aren't Pale Red Dot now studying all our local red dwarfs for planets?
AFAIK just Proxima Centauri, Barnard's Star, and Ross 154.
Out of interest what was the criteria for choosing those three out of all the red dwarfs near Sol?
Because they are visible from La Silla at this time of year and are bright enough for high-res spectroscopy.
To add to that, there has been a shift in in strategy in recent years for radial velocity surveys away from "Sample numerous stars a few times each" to "Sample a few stars numerous times each." The first one easily catches your intermediate- and long-period giant planets, but to get down to low-mass planets, you have to really drill a star to get enough data to overcome statistical noise. Detecting low-mass planets in the solar neighborhood is now finally feasible, so rather than observing all the local M dwarfs in the sky, we're focusing on hitting a few nearby, bright systems.

Thank you all. I am constantly amazed that we are able to make such fine measurements of objects so far, it almost seems remarkable.
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 08/20/2017 08:27 PM
There is a candidate for a Super Earth (https://arxiv.org/abs/1702.03571) around Lalande 21185, the 6th closest main sequence star / 4th closest star system (it's missing from CuddlyRocket's list).

I didn't include Lalande 21185 in my list because I was listing those stars not known to have a planet and this star has a pretty solid candidate. But then I forgot to adjust the ordinal numbering (Sirius should be the 7th nearest etc.)!  :-[
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 08/22/2017 07:50 AM
Dynamics of a Probable Earth-mass Planet in the GJ 832 System

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The stability of planetary orbits around the GJ 832 star system, which contains inner (GJ 832c) and outer (GJ 832b) planets, is investigated numerically and a detailed phase-space analysis is performed. Special attention is given to the existence of stable orbits for a planet less than 15 M ⊕ that is injected between the inner and outer planets. Thus, numerical simulations are performed for three and four bodies in elliptical orbits (or circular for special cases) by using a large number of initial conditions that cover the selected phase-spaces of the planet's orbital parameters. The results presented in the phase-space maps for GJ 832c indicate the least deviation of eccentricity from its nominal value, which is then used to determine its inclination regime relative to the star–outer planet plane. Also, the injected planet is found to display stable orbital configurations for at least one billion years. Then, the radial velocity curves based on the signature from the Keplerian motion are generated for the injected planets with masses 1 M ⊕ to 15 M ⊕ in order to estimate their semimajor axes and mass limits. The synthetic RV signal suggests that an additional planet of mass ≤15 M ⊕ with a dynamically stable configuration may be residing between 0.25 and 2.0 au from the star. We have provided an estimated number of RV observations for the additional planet that is required for further observational verification.

http://iopscience.iop.org/article/10.3847/1538-4357/aa80e2/meta

I have to say I find that article a bit weird. Its not like they have detected anything, not even that there is a hint in the data for the presence of an additional planet. All they have is "if there is a planet here, its orbit would be stable". Oh well - a super-Earth way inside Mercury would also be on a stable orbit, but that doesn't mean there is one. But still, you have news sites like this one (https://www.universetoday.com/136837/another-nearby-red-dwarf-star-system-another-possible-exoplanet-discovered/) running with headlines suggesting a planet has been found...
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/22/2017 04:30 PM
New Findings on Brown Dwarf Atmospheres

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I often think of brown dwarfs in terms of the planets that might form around them, and the question of whether even these small ‘failed stars’ may be capable of sustaining life. Have a look, for example, at Luhman 16AB, two brown dwarfs in the Sun’s immediate neighborhood. There are some indications of a planet here which, if it were ever confirmed, would make it the second closest known exoplanet to the Earth, at least for now. We can rule out planets of Neptune mass or greater with a period of between one and two years, but future Hubble observations, already approved for August of next year, may tell us more.

https://www.centauri-dreams.org/?p=38327
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/22/2017 07:12 PM
On reflection this seems more appropriate in this area.

Likely Transiting Exocomets Detected by Kepler

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We present the first good evidence for exocomet transits of a host star in continuum light in data from the Kepler mission. The Kepler star in question, KIC 3542116, is of spectral type F2V and is quite bright at Kp=10. The transits have a distinct asymmetric shape with a steeper ingress and slower egress that can be ascribed to objects with a trailing dust tail passing over the stellar disk. There are three deeper transits with depths of ≃0.1% that last for about a day, and three that are several times more shallow and of shorter duration. The transits were found via an exhaustive visual search of the entire Kepler photometric data set, which we describe in some detail. We review the methods we use to validate the Kepler data showing the comet transits, and rule out instrumental artifacts as sources of the signals. We fit the transits with a simple dust-tail model, and find that a transverse comet speed of ∼35-50 km s−1 and a minimum amount of dust present in the tail of ∼1016 g are required to explain the larger transits. For a dust replenishment time of ∼10 days, and a comet lifetime of only ∼300 days, this implies a total cometary mass of ≳3×1017 g, or about the mass of Halley's comet. We also discuss the number of comets and orbital geometry that would be necessary to explain the six transits detected over the four years of Kepler prime-field observations. Finally, we also report the discovery of a single comet-shaped transit in KIC 11084727 with very similar transit and host-

https://arxiv.org/abs/1708.06069
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/24/2017 12:34 AM
The META detections. Somewhat before my time so I had never heard of these before. Useful links in the description to further reading as well.

Post by: Star One on 08/24/2017 09:59 PM
The CGI in the video makes it look like it has a malevolent face, with two huge staring eyes it even has pupils!

Best Ever Image of a Star’s Surface and Atmosphere

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First map of motion of material on a star other than the Sun

Quote
Using ESO’s Very Large Telescope Interferometer astronomers have constructed the most detailed image ever of a star — the red supergiant star Antares. They have also made the first map of the velocities of material in the atmosphere of a star other than the Sun, revealing unexpected turbulence in Antares’s huge extended atmosphere. The results were published in the journal Nature.

http://www.eso.org/public/news/eso1726/

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/29/2017 07:29 PM
Likely Transiting Exocomets Detected by Kepler by Visual Lightcurve Inspection

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In January 2017, amateur astronomer Tom Jacobs proposed the idea of visually surveying the complete Q1-Q17 Kepler lightcurve archive spanning 201,250 target stars for Data Release 25 (Thompson et al. 2016) with professional astronomers Saul Rappaport and Andrew Vanderburg along with amateur astronomer Daryll LaCourse. "The survey was conducted using the LcTools software system (Kipping et al. 2015), a publicly available Windows-based set of applications designed for processing lightcurves in a fast and efficient manner. Two primary components from the system were utilized; LcGenerator for building lightcurves in bulk and LcViewer for visually inspecting plots of the lightcurve for signals of interest."

The team has worked on similar projects with the K2 campaigns. The survey lasted five months with one person (TJ) individually inspecting each lightcurve for interesting objects that were non periodic in nature. There were no predetermined search parameters. Everything was on the table and numerous flagged objects turned out to be data breaks and data processing anomalies (data glitches) upon subsequent analysis by Saul Rappaport and Andrew Vanderburg. Both veterans were indefatigable in supporting the search effort. On March 18th, KIC 35421116 was initially flagged for its three aperiodic transits and subsequently labeled and analyzed as exocomet candidates.

http://keplerlightcurves.blogspot.co.uk/2017/08/likely-transiting-exocomets-detected-by.html?m=1
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/29/2017 07:34 PM
Kepler space telescope discovers variability in the Seven Sisters

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Most of the seven stars are revealed to be slowly-pulsating B stars, a class of variable star in which the star’s brightness changes with day-long periods. The frequencies of these pulsations are key to  exploring some of the poorly understood processes in the core of these stars.

The seventh star, Maia, is different: it varies with a regular period of 10 days. Previous studies have shown that Maia belongs to a class of stars with abnormal surface concentrations of some chemical elements such as manganese. To see if these things were related, a series of spectroscopic observations were taken with the Hertzsprung SONG Telescope.

“What we saw was that the brightness changes seen by Kepler go hand-in-hand with changes in the strength of manganese absorption in Maia’s atmosphere,” said Dr. Victoria Antoci, a co-author of the work and Assistant Professor at the Stellar Astrophysics Centre, Aarhus University. “We conclude that the variations are caused by a large chemical spot on the surface of the star, which comes in and out of view as the star rotates with a ten day period.”

“Sixty years ago, astronomers had thought they could see variability in Maia with periods of a few hours and suggested this was the first of a whole new class of variable stars they called ‘Maia Variables’,” White said, “but our new observations show that Maia is not itself a Maia Variable!”

No signs of exoplanetary transits were detected in this study, but the authors show that their new algorithm can attain the precision that will be needed for Kepler and future space telescopes such as the Transiting Exoplanet Survey Satellite (TESS) to detect planets transiting stars as bright as our neighbouring star Alpha Centauri. These nearby bright stars are the best targets for future missions and facilities such as the James Webb Space Telescope, which is due to launch in late 2018.

https://astronomynow.com/2017/08/29/kepler-space-telescope-discovers-variability-in-the-seven-sisters/
Post by: Star One on 08/30/2017 07:00 PM
Exoplanet-Hunters Detect Two New “Warm Jupiters”

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The study of extra-solar planets has turned up some rather interesting candidates in the past few years. As of August 1st, 2017, a total of 3,639 exoplanets have been discovered in 2,729 planetary systems and 612 multiple planetary systems. Many of these discoveries have challenged conventional thinking about planets, especially where their sizes and distances from their suns are concerned.

According to a study by an international team of astronomers, the latest exoplanet discoveries are in keeping with this trend. Known as EPIC 211418729b and EPIC 211442297b, these two gas giants orbit stars that are located about 1569 and 1360 light-years from Earth (respectively) and are similar in size to Jupiter. Combined with their relatively close orbit to their stars, the team has designated them as “Warm Jupiters”.

The study, titled “EPIC 211418729b and EPIC 211442297b: Two Transiting Warm Jupiters“, recently appeared online. Led by Avi Shporer – a postdoctoral scholar with the Geological and Planetary Sciences (GPS) division at the California Institute of Technology (Caltech) – the team relied on data from the Kepler and K2 missions, and follow-up observations with multiple ground-based telescopes, to determine the sizes, masses and orbits of these planets.

https://www.universetoday.com/137001/exoplanet-hunters-detect-two-new-warm-jupiters/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/31/2017 05:57 AM
Distant galaxy sends out 15 high-energy radio bursts

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Breakthrough Listen, an initiative to find signs of intelligent life in the universe, has detected 15 brief but powerful radio pulses emanating from a mysterious and repeating source – FRB 121102 – far across the universe.

Fast radio bursts are brief, bright pulses of radio emission from distant but largely unknown sources, and FRB 121102 is the only one known to repeat: more than 150 high-energy bursts have been observed coming from the object, which was identified last year as a dwarf galaxy about 3 billion light years from Earth.

Possible explanations for the repeating bursts range from outbursts from rotating neutron stars with extremely strong magnetic fields – so-called magnetars – to a more speculative idea: They are directed energy sources, powerful laser bursts used by extraterrestrial civilizations to power spacecraft, akin to Breakthrough Starshot's plan to use powerful laser pulses to propel nano-spacecraft to Earth's nearest star, Proxima Centauri.

"Bursts from this source have never been seen at this high a frequency," said Andrew Siemion, director of the Berkeley SETI Research Center and of the Breakthrough Listen program.

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 08/31/2017 10:24 PM
Close encounters of the stellar kind

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Understanding the past and future motions of stars is a key goal of Gaia as it collects precise data on stellar positions and motions over its five-year mission. After 14 months, the first catalogue of more than a billion stars was recently released, which included the distances and the motions across the sky for more than two million stars.

By combining the new results with existing information, astronomers began a detailed, large-scale search for stars passing close to our sun.

So far, the motions relative to the sun of more than 300 000 stars have been traced through the galaxy and their closest approach determined for up to five million years in the past and future.

Of them, 97 stars were found that will pass within 150 trillion kilometres, while 16 come within about 60 trillion km.

While the 16 are considered reasonably near, a particularly close encounter of one star, Gliese 710, in 1.3 million years' time, stands out. It is predicted to pass within just 2.3 trillion km or about 16 000 Earth–sun distances, well within the Oort Cloud.

The star is already well-documented, and thanks to the Gaia data, the estimated encounter distance has recently been revised. Previously, there was a 90% degree of certainty that it would come within 3.1–13.6 trillion kilometres. Now, the more accurate data suggest that it will come within 1.5–3.2 trillion km, with 2.3 trillion km most likely.

Furthermore, although Gliese 710 has a mass of 60% that of our sun, it travels much slower than most stars: nearly 50 000 km/h at closest approach, compared with the average 100 000 km/h.

The speed of its passage means it will have plenty of time to exert its gravitational influence on bodies in the Oort Cloud, potentially sending showers of comets into the solar system.

Despite its slower pace, it will still appear as the brightest, fastest object in the night sky at closest approach.

https://m.phys.org/news/2017-08-encounters-stellar-kind.html
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/01/2017 07:12 PM
Asteroseismic masses of retired planet-hosting A-stars using SONG

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To better understand how planets form, it is important to study planet occurrence rates as a function of stellar mass. However, estimating masses of field stars is often difficult. Over the past decade, a controversy has arisen about the inferred occurrence rate of gas-giant planets around evolved intermediate-mass stars -- the so-called `retired A-stars'. The high masses of these red-giant planet hosts, derived using spectroscopic information and stellar evolution models, have been called into question. Here we address the controversy by determining the masses of eight evolved planet-hosting stars using asteroseismology. We compare the masses with spectroscopic-based masses from the Exoplanet Orbit Database that were previously adopted to infer properties of the exoplanets and their hosts. We find a significant one-sided offset between the two sets of masses for stars with spectroscopic masses above roughly 1.6Msun, suggestive of an average 15--20% overestimate of the adopted spectroscopic-based masses. The only star in our sample well below this mass limit is also the only one not showing this offset. Finally, we note that the scatter across literature values of spectroscopic-based masses often exceed their formal uncertainties, making it comparable to the offset we report here.

https://arxiv.org/abs/1708.09613
Post by: Star One on 09/01/2017 07:22 PM
In relation to Gliese 710 I know the Sun couldn't capture another star if it wandered close to the Solar System, but could it capture something less massive like a brown dwarf if one did the same thing?

Title: Re: Exoplanets And Stars Thread
Post by: whitelancer64 on 09/01/2017 07:55 PM
In relation to Gliese 710 I know the Sun couldn't capture another star if it wandered close to the Solar System, but could it capture something less massive like a brown dwarf if one did the same thing?

No, and for the same reason. In order to be captured, the object has to slow down. The only way for a body wandering close to our star to be captured by its gravity is for the body to exchange momentum with another body - for example, by gravitationally interacting with Jupiter and throwing it into a different orbit, or ejecting it from the Solar System entirely.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/01/2017 08:22 PM
In relation to Gliese 710 I know the Sun couldn't capture another star if it wandered close to the Solar System, but could it capture something less massive like a brown dwarf if one did the same thing?

No, and for the same reason. In order to be captured, the object has to slow down. The only way for a body wandering close to our star to be captured by its gravity is for the body to exchange momentum with another body - for example, by gravitationally interacting with Jupiter and throwing it into a different orbit, or ejecting it from the Solar System entirely.

I suppose that's why if it exists the captured planet theory is disfavoured for planet nine.
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 09/01/2017 09:33 PM
In relation to Gliese 710 I know the Sun couldn't capture another star if it wandered close to the Solar System, but could it capture something less massive like a brown dwarf if one did the same thing?

No, and for the same reason. In order to be captured, the object has to slow down. The only way for a body wandering close to our star to be captured by its gravity is for the body to exchange momentum with another body - for example, by gravitationally interacting with Jupiter and throwing it into a different orbit, or ejecting it from the Solar System entirely.

An alternative scenario is where the object that ends up being captured is part of a binary pair. This is one hypothesis for the capture of Triton by Neptune (Neptune’s capture of its moon Triton in a binary-planet gravitational encounter (http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.568.9568&rep=rep1&type=pdf) (pdf)).
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/03/2017 09:33 AM
Main reason I am posting this video is he mentions there has been further FRB detections since the announcement above. I like his videos as he keeps a level head unlike some on YouTube & generally makes statements in reference to papers he links to.

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/04/2017 04:28 PM
Supermassive black hole discovered near heart of the Milky Way

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An enormous black hole one hundred thousand times more massive than the sun has been found hiding in a toxic gas cloud wafting around near the heart of the Milky Way.

If the discovery is confirmed, the invisible behemoth will rank as the second largest black hole ever seen in the Milky Way after the supermassive black hole known as Sagittarius A* that is anchored at the very centre of the galaxy.

Quote
Oka, whose research is published in the journal Nature Astronomy, said the newly-found black hole could be the core of an old dwarf galaxy that was cannibalised during the formation of the Milky Way billions of years ago.

Quote
All of which points to the fate that awaits the newly-found black hole. In time, Oka said, the object will be drawn towards Sagittarius A* and sink into it, making the supermassive black hole at the heart of the Milky Way even more massive.

https://www.theguardian.com/science/2017/sep/04/supermassive-black-hole-discovered-near-heart-of-the-milky-way
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 09/04/2017 10:56 PM
A modified CoRoT detrend algorithm and the discovery of a new planetary companion (https://arxiv.org/abs/1709.00351)

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We present MCDA, a modification of the CoRoT detrend algorithm (CDA) suitable to detrend chromatic light curves. By means of robust statistics and better handling of short term variability, the implementation decreases the systematic light curve variations and improves the detection of exoplanets when compared with the original algorithm. All CoRoT chromatic light curves (a total of 65,655) were analysed with our algorithm. Dozens of new transit candidates and all previously known CoRoT exoplanets were rediscovered in those light curves using a box-fitting algorithm. For three of the new cases spectroscopic measurements of the candidates' host stars were retrieved from the ESO Science Archive Facility and used to calculate stellar parameters and, in the best cases, radial velocities. In addition to our improved detrend technique we announce the discovery of a planet that orbits a 0.79+0.08−0.09R⊙ star with a period of 6.71837±0.00001 days and has 0.57+0.06−0.05RJ and 0.15±0.10MJ. We also present the analysis of two cases in which parameters found suggest the existence of possible planetary companions.
Post by: Star One on 09/05/2017 08:59 AM
Quote
Large solar storms, responsible for the northern lights, may have played a role in the strandings of 29 sperm whales in the North Sea early in 2016.

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Dr Vanselow and his colleagues studied the connection between whale strandings and two major solar storms that took place at the very end of December in 2015.
These produced huge displays of the Aurora Borealis that were seen in many parts of Scotland and elsewhere.
Looking specifically at the region around Shetland, the scientists found that these solar events would have caused short-term shifts in the magnetic field of up to 460km, in the area between the islands and Norway.
This could have caused sperm whales in the region to move in the wrong direction.
They also believe that sperm whales see a regular magnetic anomaly off the Norwegian coast as a "geomagnetic mountain chain", a kind of guardrail that prevents them from entering the North Sea.
The solar storms may have nullified this effect, rendering the mountain chain invisible and allowing the whales to swim through into the North Sea.

Quote
Nasa has also been investigating the question of whether solar storms can affect a whole range of cetaceans around the world.
A team of researchers is shortly to publish a research paper on the connection between strandings in Cape Cod and geomagnetic storms. They say the Venselow paper is "well founded".
"It is one potential mechanism for having animals confused, I think it's a credible theory," Dr Antti Pulkkinen, who is leading the Nasa project, told BBC News.
"But does their paper prove that is the case? I don't think so."
"Having looked at this problem from a data analysis point of view, it is not a single factor that contributes to this.
"Things need to line up from multiple different perspectives for these events to take place."

http://www.bbc.co.uk/news/science-environment-41110082
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/05/2017 04:32 PM
The Surface UV Environment on Planets Orbiting M-Dwarfs: Implications for Prebiotic Chemistry & Need for Experimental Follow-Up

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Potentially-habitable planets orbiting M-dwarfs are of intense astrobiological interest because they are the only rocky worlds accessible to biosignature search over the next 10+ years due to a confluence of observational effects. Simultaneously, recent experimental and theoretical work suggests that UV light may have played a key role in the origin of life on Earth, and especially the origin of RNA. Characterizing the UV environment on M-dwarfs planets is important to understanding whether life as we know it could emerge on such worlds. In this work, we couple radiative transfer models to observed M-dwarf spectra to determine the UV environment on prebiotic Earth-analog planets orbiting M-dwarfs. We calculate dose rates to quantify the impact of different host stars on prebiotically-important photoprocesses. We find that M-dwarf planets have access to 100-1000 times less bioactive UV fluence than the young Earth. It is unclear whether UV-sensitive prebiotic chemistry that may have been important to abiogenesis, such as the only known prebiotically plausible pathways for pyrimidine ribonucleotide synthesis, could function on M-dwarf planets. This uncertainty affects objects like the recently-discovered habitable-zone planets orbiting Proxima Centauri, TRAPPIST-1, and LHS 1140. Laboratory studies of the sensitivity of putative prebiotic pathways to irradiation level are required to resolve this uncertainty. If steady-state M-dwarf UV output is insufficient to power these pathways, transient elevated UV irradiation due to flares may suffice; laboratory studies can constrain this possibility as well.

https://arxiv.org/abs/1705.02350
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/05/2017 09:46 PM
Shocking discovery explains powerful novae

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Employing two powerful telescopes, astronomers at Michigan State University have proven a theory that explains these super-luminous novae and other astronomical explosions. The results, published in the current issue of Nature Astronomy, indicate that powerful shockwaves amplify the explosions beyond any traditional scale for nuclear explosions.

“Astronomers have long thought the energy from novae was dominated by the white dwarf, controlling how much light and energy are emitted,” said Laura Chomiuk, MSU astronomer and study co-author. “What we discovered, however, was a completely different source of energy — shockwaves that can dominate the entire explosion.”

As the explosion begins, it ejects a cooler, slower wave of gaseous material, relatively speaking. Behind it, though, is a hot, fast wave speeding right behind it. The collision of the two ejections produces a shockwave, which results in a spectacular explosion of heat and light.

“The bigger the shock, the brighter the nova,” Chomiuk said. “We believe it’s the speed of the second wave that influences the explosion.”

This study explains a theory held by Brian Metzger, Columbia University astronomer, who also is a co-author for this paper.

Now that the theory has been proven, astronomers use novae to better understand other super-charged explosions, like those that mark the death of massive stars in galaxies far away.

https://astronomynow.com/2017/09/05/shocking-discovery-explains-powerful-novae/
Post by: Star One on 09/06/2017 07:09 PM
X-rays reveal temperament of possible planet-hosting stars

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A new X-ray study has revealed that stars like the Sun and their less massive cousins calm down surprisingly quickly after a turbulent youth. This result has positive implications for the long-term habitability of planets orbiting such stars.

https://astronomynow.com/2017/09/06/x-rays-reveal-temperament-of-possible-planet-hosting-stars/

Study of Uranus suggests some of its moons are on a collision course

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In studying the orbits of the moons, the researchers found that Cressida is on a path that will cause it to collide with another moon called Desdemona, which currently moves in an orbit just 900 kilometers from Cressida's. The gravity of Cressida is slowly pulling them closer together and will cause them to crash into one another in approximately 1 million years. They also found the same to be true for Cupid and Belinda, which will collide sometime later.

The researchers note that material in the inner rings around Uranus appears likely to be the remnants of other moons that were destroyed when they collided.

https://phys.org/news/2017-09-uranus-moons-collision.amp
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/07/2017 04:41 PM
Astrometric exoplanet detectability and the Earth orbital motion

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Astrometric exoplanet discovery relies on detection of stellar motion caused by planetary companions. Systems with orbital period close to one year may escape detection if orbital motion of their host stars are observationally indistinguishable from parallax effect. Additionally, astrometric solution may produce a biased parallax estimation for such systems. We examine effects of orbital motion of the Earth on astrometric detectability in terms of correlation between the Earth's orbital position and position of the star relative to system barycentre. The χ2 statistic for parallax estimation is calculated analytically, leading to expressions that relate the decrease in detectability and accompanying parallax bias to the position correlation function. The effects of the Earth motion's critically depend on orbital period, diminishing rapidly as period deviates from one year. Selection effects against one-year period systems is therefore expected. Statistical estimation shows that corresponding loss of sensitivity is equivalent to a 10 per cent increase in detection threshold. Consideration of eccentric orbits shows that the Earth's motion has no effect on detectability for e≥0.5. Dependence of detectability on other parameters, such as orbital phases and inclination of the orbit plane to the ecliptic, are smooth and monotonic because they are described by simple trigonometric functions.

https://arxiv.org/abs/1709.00290
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/07/2017 07:16 PM
Extreme’ telescopes find the second-fastest-spinning pulsar

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By following up on mysterious high-energy sources mapped out by NASA’s Fermi Gamma-ray Space Telescope, the Netherlands-based Low Frequency Array (LOFAR) radio telescope has identified a pulsar spinning at more than 42,000 revolutions per minute, making it the second-fastest known.

https://astronomynow.com/2017/09/06/extreme-telescopes-find-the-second-fastest-spinning-pulsar/
Title: Re: Exoplanets And Stars Thread
Post by: hop on 09/08/2017 07:19 AM
A fun one: From what stars are we a transiting planet?

Transit Visibility Zones of the Solar System Planets (https://arxiv.org/abs/1709.02211) R. Wells, K. Poppenhaeger, C. A. Watson, R. Heller

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The detection of thousands of extrasolar planets by the transit method naturally raises the question of whether potential extrasolar observers could detect the transits of the Solar System planets. We present a comprehensive analysis of the regions in the sky from where transit events of the Solar System planets can be detected. We specify how many different Solar System planets can be observed from any given point in the sky, and find the maximum number to be three. We report the probabilities of a randomly positioned external observer to be able to observe single and multiple Solar System planet transits; specifically, we find a probability of 2.518% to be able to observe at least one transiting planet, 0.229% for at least two transiting planets, and 0.027% for three transiting planets. We identify 68 known exoplanets that have a favourable geometric perspective to allow transit detections in the Solar System and we show how the ongoing K2 mission will extend this list. We use occurrence rates of exoplanets to estimate that there are 3.2±1.2 and 6.6+1.3−0.8 temperate Earth-sized planets orbiting GK and M dwarf stars brighter than V=13 and V=16 respectively, that are located in the Earth's transit zone.
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 09/08/2017 11:00 PM
A System of Three Super Earths Transiting the Late K-Dwarf GJ 9827 at Thirty Parsecs (https://arxiv.org/abs/1709.01957) (arXiv)

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We report the discovery of three small transiting planets orbiting GJ 9827, a bright (K = 7.2) nearby late K-type dwarf star. GJ 9827 hosts a 1.64+0.22−0.20 R⊕ super Earth on a 1.2 day period, a 1.29+0.17−0.16 R⊕ super Earth on a 3.6 day period, and a 2.08+0.28−0.26 R⊕ super Earth on a 6.2 day period. The radii of the planets transiting GJ 9827 span the transition between predominantly rocky and gaseous planets, and GJ 9827 b and c fall in or close to the known gap in the radius distribution of small planets between these populations. At a distance of ∼30 parsecs, GJ 9827 is the closest exoplanet host discovered by K2 to date, making these planets well-suited for atmospheric studies with the upcoming James Webb Space Telescope. The GJ 9827 system provides a valuable opportunity to characterize interior structure and atmospheric properties of coeval planets spanning the rocky to gaseous transition.

The 'known gap' is the so-called Fulton Gap. I guess the name hasn't stuck with the wider astronomical community (yet?). :)
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/11/2017 07:15 PM
Gravitational Waves will let us see Inside Stars as Supernovae Happen

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However, according to a team of astronomers from Glasgow and Arizona, astronomers need not limit themselves to detecting waves caused by massive gravitational mergers. According to a study they recently produced, the Advanced LIGO, GEO 600, and Virgo gravitational-wave detector network could also detect the gravitational waves created by supernova. In so doing, astronomers will able to see inside the hearts of collapsing stars for the first time.

The study, titled “Inferring the Core-Collapse Supernova Explosion Mechanism with Three-Dimensional Gravitational-Wave Simulations“, recently appeared online. Led by Jade Powell, who recently finished her PhD at the Institute for Gravitational Research at the University of Glasgow, the team argue that current gravitational wave experiments should be able to detect the waves created by Core Collapse Supernovae (CSNe).

https://www.universetoday.com/137068/gravitational-waves-will-let-us-see-inside-stars-supernovae-happen/amp/
Title: Re: Exoplanets And Stars Thread
Post by: redliox on 09/12/2017 12:06 AM
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?
Title: Re: Exoplanets And Stars Thread
Post by: jebbo on 09/12/2017 11:07 AM
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?

You really don't need that large a telescope (assuming space based).  The key things are the Inner Working Angle and contrast ratio between the star and planet.

For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:

--- Tony
Title: Re: Exoplanets And Stars Thread
Post by: redliox on 09/12/2017 06:11 PM
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?

You really don't need that large a telescope (assuming space based).  The key things are the Inner Working Angle and contrast ratio between the star and planet.

For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:

--- Tony

That's hopeful.  I believe I can understand what you mean by ratio (such as how a bright distant Jupiter might be easier to detect that a dark SuperEarth), but elaborate on IWA.  What else would allow an exoplanet to be more than a pixel in an image as well?
Title: Re: Exoplanets And Stars Thread
Post by: as58 on 09/12/2017 07:40 PM
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?

You really don't need that large a telescope (assuming space based).  The key things are the Inner Working Angle and contrast ratio between the star and planet.

For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:

--- Tony

That's hopeful.  I believe I can understand what you mean by ratio (such as how a bright distant Jupiter might be easier to detect that a dark SuperEarth), but elaborate on IWA.  What else would allow an exoplanet to be more than a pixel in an image as well?

IWA is the smallest angle where at least 50% percent of the light is transmitted by the coronagraph; at smaller angles most of the light from the planet is blocked along with stellar light. Best coronagraph designs achieve IWA of about 2*lambda/D. But if you mean by "resolving" seeing the planet as something other than just a single pixel, much bigger telescopes are needed.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/13/2017 08:48 PM
Boiling exoplanet has titanium atmosphere

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The exoplanet WASP-19b has huge amounts of titanium oxide in its atmosphere, causing the atmosphere to 'reverse' so some of the upper layers are warmer than those lower down.

http://m.skyatnightmagazine.com/news/boiling-exoplanet-has-titanium-atmosphere
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/15/2017 07:18 PM
NASA's Hubble Captures Blistering Pitch-Black Planet
NASA's Hubble Space Telescope has observed a planet outside our solar system that looks as black as fresh asphalt because it eats light rather than reflecting it back into space. This light-eating prowess is due to the planet's unique capability to trap at least 94 percent of the visible starlight falling into its atmosphere.

The oddball exoplanet, called WASP-12b, is one of a class of so-called "hot Jupiters," gigantic, gaseous planets that orbit very close to their host star and are heated to extreme temperatures. The planet's atmosphere is so hot that most molecules are unable to survive on the blistering day side of the planet, where the temperature is 4,600 degrees Fahrenheit. Therefore, clouds probably cannot form to reflect light back into space. Instead, incoming light penetrates deep into the planet's atmosphere where it is absorbed by hydrogen atoms and converted to heat energy.

"We did not expect to find such a dark exoplanet," said Taylor Bell of McGill University and the Institute for Research on Exoplanets in Montreal, Quebec, Canada, lead researcher of the Hubble study. "Most hot Jupiters reflect about 40 percent of starlight."

But the planet's nighttime side is a different story. WASP-12b has a fixed day side and night side because it orbits so close to the star that it is tidally locked. The nighttime side is more than 2,000 degrees Fahrenheit cooler, which allows water vapor and clouds to form. Previous Hubble observations of the day/night boundary detected evidence of water vapor and possibly clouds and hazes in the atmosphere. WASP-12b is about 2 million miles away from its star and completes an orbit once a day.

"This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters," Bell said. "You can have planets like WASP-12b that are 4,600 degrees Fahrenheit and some that are 2,200 degrees Fahrenheit, and they're both called hot Jupiters. Past observations of hot Jupiters indicate that the temperature difference between the day and night sides of the planet increases with hotter day sides. This previous research suggests that more heat is being pumped into the day side of the planet, but the processes, such as winds, that carry the heat to the night side of the planet don't keep up the pace."

The researchers determined the planet's light-eating capabilities by using Hubble's Space Telescope Imaging Spectrograph to search in mostly visible light for a tiny dip in starlight as the planet passed directly behind the star. The amount of dimming tells astronomers how much reflected light is given off by the planet. However, the observations did not detect reflected light, meaning that the daytime side of the planet is absorbing almost all the starlight falling onto it.

First spotted in 2008, WASP-12b circles a Sun-like star residing 1,400 light-years away in the constellation Auriga. Since its discovery, several telescopes have studied the exoplanet, including Hubble, NASA's Spitzer Space Telescope, and NASA's Chandra X-ray Observatory. Previous observations by Hubble's Cosmic Origins Spectrograph (COS) revealed that the planet may be downsizing. COS detected material from the planet's super-heated atmosphere spilling onto the star.

The results appear in the Sept. 14 issue of The Astrophysical Journal Letters.

https://www.nasa.gov/feature/goddard/2017/hubble-captures-blistering-pitch-black-planet
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 09/15/2017 10:22 PM
Bayesian Analysis of Hot Jupiter Radius Anomalies: Evidence for Ohmic Dissipation? (https://arxiv.org/abs/1709.04539) (arXiv)

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The cause of hot Jupiter radius inflation, where giant planets with Teq >1000 K are significantly larger than expected, is an open question and the subject of many proposed explanations. Rather than examine these models individually, this work seeks to characterize the anomalous heating as a function of incident flux, ϵ(F), needed to inflate the population of planets to their observed sizes. We then compare that result to theoretical predictions for various models. We examine the population of about 300 giant planets with well-determined masses and radii and apply thermal evolution and Bayesian statistical models to infer the anomalous power as a function of incident flux that best reproduces the observed radii. First, we observe that the inflation of planets below about M=0.5MJ appears very different than their higher mass counterparts, perhaps as the result of mass loss or an inefficient heating mechanism. As such, we exclude planets below this threshold. Next, we show with strong significance that ϵ(F) increases with Teq towards a maximum of ∼2.5% at Teq≈1500 K, and then decreases as temperatures increase further, falling to ∼0.2% at Teff=2500 K. This high-flux decrease in inflation efficiency was predicted by the Ohmic dissipation model of giant planet inflation but not other models. We also explicitly check the thermal tides model and find that it predicts far more variance in radii than is observed. Thus, our results provide evidence for the Ohmic dissipation model and a functional form for ϵ(F) that any future theories of hot Jupiter radii can be tested against.

It's interesting that exoplanet studies are quickly finding these apparent physical boundaries separating planets into different classes.
Post by: Star One on 09/17/2017 07:05 PM
Diamonds Really Do Rain on Neptune, Experiments Conclude

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Researchers subjected hydrocarbon samples in a laboratory to Neptune-like pressures. The samples, reminiscent of molecules found in the ice giant’s atmosphere, compressed into nanodiamonds.

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Knowing how hydrocarbons might behave deep within an ice giant’s atmosphere will affect our understanding of how atmospheres transport heat and evolve over time, explained Kraus. What’s more, the implications of this research extend beyond our solar system to exoplanets, as a large fraction of the known exoplanets are similar in size or mass to our ice giants.

The ability to model an ice giant atmosphere’s density from the top down to the core is a critical part of characterizing that planet. For example, an atmosphere made mostly of hydrogen is much puffier than one with diamonds, Kraus noted.

A diamond-studded atmosphere also likely behaves very differently than one without diamonds. For example, atmospheric convection might have to overcome more hurdles, which may lead to sharp changes in chemical composition between different atmospheric layers, the researchers said. This could also inhibit heat flow.

“These experiments can be used to improve our understanding of the behavior of common materials in the universe at high pressures and temperatures, which has a direct connection to modeling planetary interiors,” said Ravit Helled, a computational science and theoretical astrophysics professor at the University of Zurich in Switzerland, who was not involved in the study.

https://eos.org/articles/diamonds-really-do-rain-on-neptune-experiments-conclude
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/18/2017 08:04 PM
Do planets remember how they formed?

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One of the most directly observable features of a transiting multi-planet system is their size-ordering when ranked in orbital separation. Kepler has revealed a rich diversity of outcomes, from perfectly ordered systems, like Kepler-80, to ostensibly disordered systems, like Kepler-20. Under the hypothesis that systems are born via preferred formation pathways, one might reasonably expect non-random size-orderings reflecting these processes. However, subsequent dynamical evolution, often chaotic and turbulent in nature, may erode this information and so here we ask - do systems remember how they formed? To address this, we devise a model to define the entropy of a planetary system's size-ordering, by first comparing differences between neighboring planets and then extending to accommodate differences across the chain. We derive closed-form solutions for many of the micro state occupancies and provide public code with look-up tables to compute entropy for up to ten-planet systems. All three proposed entropy definitions exhibit the expected property that their credible interval increases with respect to a proxy for time. We find that the observed Kepler multis display a highly significant deficit in entropy compared to a randomly generated population. Incorporating a filter for systems deemed likely to be dynamically packed, we show that this result is robust against the possibility of missing planets too. Put together, our work establishes that Kepler systems do indeed remember something of their younger years and highlights the value of information theory for exoplanetary science.

https://arxiv.org/abs/1709.04987
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/18/2017 08:30 PM
New supernova analysis reframes dark energy debate

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The accelerating expansion of the universe may not be real, but could just be an apparent effect, according to new research published in the journal Monthly Notices of the Royal Astronomical Society. The new study — by a group at the University of Canterbury in Christchurch, New Zealand — finds the fit of Type Ia supernovae to a model universe with no dark energy to be very slightly better than the fit to the standard dark energy model.

https://astronomynow.com/2017/09/18/new-supernova-analysis-reframes-dark-energy-debate/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/21/2017 04:03 PM
The empty primordial asteroid belt

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Abstract
The asteroid belt contains less than a thousandth of Earth’s mass and is radially segregated, with S-types dominating the inner belt and C-types the outer belt. It is generally assumed that the belt formed with far more mass and was later strongly depleted. We show that the present-day asteroid belt is consistent with having formed empty, without any planetesimals between Mars and Jupiter’s present-day orbits. This is consistent with models in which drifting dust is concentrated into an isolated annulus of terrestrial planetesimals. Gravitational scattering during terrestrial planet formation causes radial spreading, transporting planetesimals from inside 1 to 1.5 astronomical units out to the belt. Several times the total current mass in S-types is implanted, with a preference for the inner main belt. C-types are implanted from the outside, as the giant planets’ gas accretion destabilizes nearby planetesimals and injects a fraction into the asteroid belt, preferentially in the outer main belt. These implantation mechanisms are simple by-products of terrestrial and giant planet formation. The asteroid belt may thus represent a repository for planetary leftovers that accreted across the solar system but not in the belt itself.

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/22/2017 09:22 AM

Astronomers Have Spotted a Strange Hybrid Asteroid in Our Solar System

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The Hubble space telescope has seen a lot of weird things that defy easy definition. Here's one more for the list – a binary asteroid that's also a comet.

Astronomers have found a pair of them, in fact, swirling around one another in the asteroid belt while leaving a stream of dust in their wake. Not only is it a beautiful example of how nature DNGAF about our categories, it raises some interesting questions on how many of these hybrids might be out there.

The binary object itself was first spotted back in 2006 as part of the asteroid-searching Spacewatch program, resulting in it getting the not-so-glamorous name 2006 VW139.

It wasn't until 2012 that astronomers realised something odd about it; this thing that was an asteroid with comet-like characteristics, namely a streaming tail.

So-called main belt comets aren't new, but they're by no means common either. This asteroid is just one of about a dozen such objects ever discovered.

What makes this particular one so unique is that it's in two pieces.

2006 VW139 is made of a pair of equal-sized lumps orbiting one another at a distance of just under 100 kilometres (about 60 miles).

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/22/2017 04:46 PM
A Fast Radio Burst Occurs Every Second throughout the Observable Universe

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Abstract
Recent multi-telescope observations of the repeating fast radio burst (FRB) FRB 121102 reveal a Gaussian-like spectral profile and associate the event with a dwarf metal-poor galaxy at a cosmological redshift of 0.19. Assuming that this event represents the entire FRB population, we make predictions for the expected number counts of FRBs observable by future radio telescopes between 50 MHz and 3.5 GHz. We vary our model assumptions to bracket the expected rate of FRBs and find that it exceeds one FRB per second per sky when accounting for faint sources. We show that future low-frequency radio telescopes, such as the Square Kilometre Array, could detect more than one FRB per minute over the entire sky originating from the epoch of reionization.

http://iopscience.iop.org/article/10.3847/2041-8213/aa8905/meta
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/25/2017 08:07 PM
Star nicknamed Kronos after eating its own planetary children

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A sun-like star seems to have devoured some of its own planetary offspring, prompting researchers to nickname it after the titan Kronos from Greek mythology.

The star HD 240430 is part of a binary system with HD 240429, and the two have now been nicknamed Kronos and Krios. The pair travel through the galaxy side by side some 320 light years from Earth.

They both seem to be about 4 billion years old, suggesting they were born from the same interstellar cloud, and initially shared the same chemical make-up.

But an analysis by Semyeong Oh at Princeton University and her team suggests the twins have led very different lives. Krios has noticeably smaller concentrations of elements like lithium, magnesium and iron floating in its atmosphere than its companion Kronos does.

In fact, the stars are more chemically different than any pair yet discovered. “I initially thought these two stars must not be in a binary,” says Oh.

https://www.newscientist.com/article/2148182-star-nicknamed-kronos-after-eating-its-own-planetary-children/
Title: Re: Exoplanets And Stars Thread
Post by: redliox on 09/26/2017 01:43 AM
Star nicknamed Kronos after eating its own planetary children

Quote
A sun-like star seems to have devoured some of its own planetary offspring, prompting researchers to nickname it after the titan Kronos from Greek mythology.

The star HD 240430 is part of a binary system with HD 240429, and the two have now been nicknamed Kronos and Krios. The pair travel through the galaxy side by side some 320 light years from Earth.

They both seem to be about 4 billion years old, suggesting they were born from the same interstellar cloud, and initially shared the same chemical make-up.

But an analysis by Semyeong Oh at Princeton University and her team suggests the twins have led very different lives. Krios has noticeably smaller concentrations of elements like lithium, magnesium and iron floating in its atmosphere than its companion Kronos does.

In fact, the stars are more chemically different than any pair yet discovered. “I initially thought these two stars must not be in a binary,” says Oh.

https://www.newscientist.com/article/2148182-star-nicknamed-kronos-after-eating-its-own-planetary-children/

Considering these theories are applicable to our own solar system's migrating planets, could there be a way to chemically discern how many planets the sun may have consumed in the past?
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/26/2017 04:56 PM
Quote
Comparative exoplanetology? That’s the striking term that Angelos Tsiaras, lead author of a new paper on exoplanet atmospheres, uses to describe the field today. Kepler’s valuable statistical look at a crowded starfield has given us insights into the sheer range of outcomes around other stars, but we’re already moving into the next phase, studying planetary atmospheres. And as the Tsiaras paper shows, constructing the first atmospheric surveys.

Tsiaras (University College, London) assembled a team of European researchers that examined 30 exoplanets, constructing their spectral profiles and analyzing them to uncover the characteristic signatures of the gases present. The study found atmospheres around 16 ‘hot Jupiters,’ learning that water vapor was present in each of them. Says Tsiaras:

“More than 3,000 exoplanets have been discovered but, so far, we’ve studied their atmospheres largely on an individual, case-by-case basis. Here, we’ve developed tools to assess the significance of atmospheric detections in catalogues of exoplanets. This kind of consistent study is essential for understanding the global population and potential classifications of these foreign worlds.”

https://www.centauri-dreams.org/?p=38547
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/27/2017 09:00 AM
Most Super-Earths Are Likely Not Habitable

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The tendency of planets to migrate early in a solar system’s history—like a planetary billiards game—would preclude the kind of stable environments that life needs to evolve. And a primitive, hydrogen-helium atmosphere would be very challenging for life. Exceptions to this general principle may still exist. For example, a planet’s original atmosphere can be lost due to radiation or impacts, as happened on Earth.

Even so, it seems that Earth’s mass is close to the optimum for a life-hosting planet. Given the new modeling results and insights, it also appears that most Super-Earths are likely not to be habitable. In the end, however, only observations will answer this question for certain. Fortunately, we should able to determine the atmospheric compositions of some Super-Earth planets within a decade.

Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/27/2017 07:10 PM
NEWLY DISCOVERED STAR CLUSTER ANALYZED BY GAIA PROBE

https://www.universetoday.com/137305/newly-discovered-star-cluster-analyzed-gaia-probe/

Paper:

https://arxiv.org/pdf/1709.04022.pdf
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 09/30/2017 10:04 AM
NASA's Hubble Observes the Farthest Active Inbound Comet Yet Seen

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NASA's Hubble Space Telescope has photographed the farthest active inbound comet ever seen, at a whopping distance of 1.5 billion miles from the Sun (beyond Saturn's orbit). Slightly warmed by the remote Sun, it has already begun to develop an 80,000-mile-wide fuzzy cloud of dust, called a coma, enveloping a tiny, solid nucleus of frozen gas and dust. These observations represent the earliest signs of activity ever seen from a comet entering the solar system's planetary zone for the first time.

The comet, called C/2017 K2 (PANSTARRS) or "K2", has been travelling for millions of years from its home in the frigid outer reaches of the solar system, where the temperature is about minus 440 degrees Fahrenheit. The comet's orbit indicates that it came from the Oort Cloud, a spherical region almost a light-year in diameter and thought to contain hundreds of billions of comets. Comets are the icy leftovers from the formation of the solar system 4.6 billion years ago and therefore pristine in icy composition.

"K2 is so far from the Sun and so cold, we know for sure that the activity — all the fuzzy stuff making it look like a comet — is not produced, as in other comets, by the evaporation of water ice," said lead researcher David Jewitt of the University of California, Los Angeles. "Instead, we think the activity is due to the sublimation [a solid changing directly into a gas] of super-volatiles as K2 makes its maiden entry into the solar system's planetary zone. That's why it's special. This comet is so far away and so incredibly cold that water ice there is frozen like a rock."

Based on the Hubble observations of K2's coma, Jewitt suggests that sunlight is heating frozen volatile gases - such as oxygen, nitrogen, carbon dioxide, and carbon monoxide - that coat the comet's frigid surface. These icy volatiles lift off from the comet and release dust, forming the coma. Past studies of the composition of comets near the Sun have revealed the same mixture of volatile ices.

"I think these volatiles are spread all through K2, and in the beginning billions of years ago, they were probably all through every comet presently in the Oort Cloud," Jewitt said. "But the volatiles on the surface are the ones that absorb the heat from the Sun, so, in a sense, the comet is shedding its outer skin. Most comets are discovered much closer to the Sun, near Jupiter's orbit, so by the time we see them, these surface volatiles have already been baked off. That's why I think K2 is the most primitive comet we've seen."

K2 was discovered in May 2017 by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii, a survey project of NASA's Near-Earth Object Observations Program. Jewitt used Hubble's Wide Field Camera 3 at the end of June to take a closer look at the icy visitor.

Hubble's sharp "eye" revealed the extent of the coma and also helped Jewitt estimate the size of the nucleus — less than 12 miles across — though the tenuous coma is 10 Earth diameters across.

This vast coma must have formed when the comet was even farther away from the Sun. Digging through archival images, Jewitt's team uncovered views of K2 and its fuzzy coma taken in 2013 by the Canada-France-Hawaii Telescope (CFHT) in Hawaii. But the object was then so faint that no one noticed it.

"We think the comet has been continuously active for at least four years," Jewitt said. "In the CFHT data, K2 had a coma already at 2 billion miles from the Sun, when it was between the orbits of Uranus and Neptune. It was already active, and I think it has been continuously active coming in. As it approaches the Sun, it's getting warmer and warmer, and the activity is ramping up."

But, curiously, the Hubble images do not show a tail flowing from K2, which is a signature of comets. The absence of such a feature indicates that particles lifting off the comet are too large for radiation pressure from the Sun to sweep them back into a tail.

Astronomers will have plenty of time to conduct detailed studies of K2. For the next five years, the comet will continue its journey into the inner solar system before it reaches its closest approach to the Sun in 2022 just beyond Mars' orbit. "We will be able to monitor for the first time the developing activity of a comet falling in from the Oort Cloud over an extraordinary range of distances," Jewitt said. "It should become more and more active as it nears the Sun and presumably will form a tail."

Jewitt said that NASA's James Webb Space Telescope, an infrared observatory scheduled to launch in 2018, could measure the heat from the nucleus, which would give astronomers a more accurate estimate of its size.

The team's results will appear in the September 28 issue of The Astrophysical Journal Letters.

http://hubblesite.org/news_release/news/2017-40
Title: Re: Exoplanets And Stars Thread
Post by: hop on 09/30/2017 10:01 PM
Paper the article above about C/2017 K2 (PANSTARRS) refers to
A Comet Active Beyond the Crystallization Zone  (https://arxiv.org/abs/1709.10079) David Jewitt, Man-To Hui, Max Mutchler, Harold Weaver, Jing Li, Jessica Agarwal

Quote
We present observations showing in-bound long-period comet We present observations showing in-bound long-period comet C/2017 K2 (PANSTARRS) to be active at record heliocentric distance. Nucleus temperatures are too low (60 K to 70 K) either for water ice to sublimate or for amorphous ice to crystallize, requiring another source for the observed activity. Using the Hubble Space Telescope we find a sharply-bounded, circularly symmetric dust coma 105 km in radius, with a total scattering cross section of ∼105 km2. The coma has a logarithmic surface brightness gradient -1 over much of its surface, indicating sustained, steady-state dust production. A lack of clear evidence for the action of solar radiation pressure suggests that the dust particles are large, with a mean size ≳ 0.1 mm. Using a coma convolution model, we find a limit to the apparent magnitude of the nucleus V> 25.2 (absolute magnitude H> 12.9). With assumed geometric albedo pV = 0.04, the limit to the nucleus circular equivalent radius is < 9 km. Pre-discovery observations from 2013 show that the comet was also active at 23.7 AU heliocentric distance. While neither water ice sublimation nor exothermic crystallization can account for the observed distant activity, the measured properties are consistent with activity driven by sublimating supervolatile ices such as CO2, CO, O2 and N2. Survival of supervolatiles at the nucleus surface is likely a result of the comet's recent arrival from the frigid Oort cloud. to be active at record heliocentric distance. Nucleus temperatures are too low (60 K to 70 K) either for water ice to sublimate or for amorphous ice to crystallize, requiring another source for the observed activity. Using the Hubble Space Telescope we find a sharply-bounded, circularly symmetric dust coma 105 km in radius, with a total scattering cross section of ∼105 km2. The coma has a logarithmic surface brightness gradient -1 over much of its surface, indicating sustained, steady-state dust production. A lack of clear evidence for the action of solar radiation pressure suggests that the dust particles are large, with a mean size ≳ 0.1 mm. Using a coma convolution model, we find a limit to the apparent magnitude of the nucleus V> 25.2 (absolute magnitude H> 12.9). With assumed geometric albedo pV = 0.04, the limit to the nucleus circular equivalent radius is < 9 km. Pre-discovery observations from 2013 show that the comet was also active at 23.7 AU heliocentric distance. While neither water ice sublimation nor exothermic crystallization can account for the observed distant activity, the measured properties are consistent with activity driven by sublimating supervolatile ices such as CO2, CO, O2 and N2. Survival of supervolatiles at the nucleus surface is likely a result of the comet's recent arrival from the frigid Oort cloud.
Title: Re: Exoplanets And Stars Thread
Post by: missinglink on 10/02/2017 03:04 AM
enveloping a tiny, solid nucleus of frozen gas and dust . . .  estimate the size of the nucleus — less than 12 miles across
Twelve miles! Not so tiny. That could really ruin someone's day if it hits. Why worry about asteroids when comets are faster, bigger . . . and currently unstoppable even by targeted nukes.
Title: Re: Exoplanets And Stars Thread
Post by: bolun on 10/03/2017 09:27 AM
BIOMARKER FOUND IN SPACE COMPLICATES SEARCH FOR LIFE ON EXOPLANETS

http://sci.esa.int/rosetta/59625-biomarker-found-in-space-complicates-search-for-life-on-exoplanets/

Quote
A molecule once thought to be a useful marker for life as we know it has been discovered around a young star and at a comet for the first time, suggesting these ingredients are inherited during the planet-forming phase.

The discovery of methyl chloride was made by the ground-based Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and by ESA's Rosetta spacecraft following Comet 67P/Churyumov-Gerasimenko. It is the simplest member of a class of molecules known as organohalogens, which contain halogens, such as chlorine or fluorine, bonded with carbon.

Methyl chloride is well known on Earth as being used in industry. It is also produced naturally by biological and geological activity: it is the most abundant organohalogen in Earth's atmosphere, with up to three megatonnes produced a year, primarily from biological processes.

As such, it had been identified as a possible 'biomarker' in the search for life at exoplanets. This has been called into question, however, now it is seen in environments not derived from living organisms, and instead as a raw ingredient from which planets could eventually form.

This is also the first time an organohalogen has been detected in space, indicating that halogen- and carbon-centred chemistries are more intertwined than previously thought.
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 10/08/2017 08:25 PM
Exterior Companions to Hot Jupiters Orbiting Cool Stars are Coplanar (https://arxiv.org/abs/1710.01737) (arXiv)
(Juliette C. Becker, Andrew Vanderburg, Fred C. Adams, Tali Khain, Marta Bryan)

Quote
The existence of hot Jupiters has challenged theories of planetary formation since the first extrasolar planets were detected. Giant planets are generally believed to form far from their host stars, where volatile materials like water exist in their solid phase, making it easier for giant planet cores to accumulate. Several mechanisms have been proposed to explain how giant planets can migrate inward from their birth sites to short-period orbits. One such mechanism, called Kozai-Lidov migration, requires the presence of distant companions in orbits inclined by more than ∼40 degrees with respect to the plane of the hot Jupiter's orbit. The high occurrence rate of wide companions in hot Jupiter systems lends support to this theory for migration. However, the exact orbital inclinations of these detected planetary and stellar companions is not known, so it is not clear whether the mutual inclination of these companions is large enough for the Kozai-Lidov process to operate. This paper shows that in systems orbiting cool stars with convective outer layers, the orbits of most wide planetary companions to hot Jupiters must be well aligned with the orbits of the hot Jupiters and the spins of the host stars. For a variety of possible distributions for the inclination of the companion, the width of the distribution must be less than ∼20 degrees to recreate the observations with good fidelity. As a result, the companion orbits are likely well-aligned with those of the hot Jupiters, and the Kozai-Lidov mechanism does not enforce migration in these systems.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/09/2017 04:41 PM
A 'Pale Green Dot': Why Proxima Centauri b May Have a Shiny Tint

Quote
A world orbiting the sun's closest stellar neighbor may have a shiny green tint to it — and not necessarily because it's covered in leafy plants.

Researchers have found a way to characterize potential auroras on the nearby exoplanet Proxima Centauri b and found that, if the planet sports oxygen in its atmosphere, the auroras may give the atmosphere a greenish cast.

"The northern and southern lights [on Proxima Centauri b] would be at least 100 times brighter than on Earth," Rodrigo Luger, a postdoctoral student at the University of Washington, who led the study of how the planet's auroras could be spotted from Earth, told Space.com by email. Luger said the auroras might be so bright as to be visible with very powerful telescopes. [Proxima b By the Numbers: Possibly Earth-Like World at the Next Star Over]

https://www.space.com/38397-proxima-centauri-planet-could-be-green.html
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/09/2017 07:24 PM
Scientists Just Found Half of the Missing Matter in Our Universe

Quote
Two teams of astronomers have found a way to observe the presence of the missing matter connecting the galaxies in the universe. This discovery can improve our understanding of how galaxies were formed in the years following the Big Bang.

https://futurism.com/scientists-just-found-half-of-the-missing-matter-in-our-universe/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/10/2017 03:26 PM
Astronomers find a Neptune-sized exoplanet in a binary star system

Quote
Using NASA's prolonged Kepler mission, known as K2, astronomers have discovered a new Neptune-sized planet in a binary star system in the Hyades open cluster. The newly found exoworld, designated K2-nnnA b, is the first known Neptune-sized planet in a binary system within an open cluster. The finding was reported Sept. 29 in a paper published on the arXiv pre-print server.

K2-nnnA b was initially spotted during K2's Campaign 13, conducted between March 8 and May 27, 2017. During this campaign, a team of astronomers led by David R. Ciardi of the California Institute of Technology (Caltech) observed a binary system named EPIC 247589423 consisting of a K-dwarf star and a late M-dwarf companion. As a result, the researchers identified a transit signal in the light curve of the binary.

https://m.phys.org/news/2017-10-astronomers-neptune-sized-exoplanet-binary-star.html
Post by: Star One on 10/11/2017 07:40 PM
Distant dwarf planet near Pluto has a ring that no one expected

Quote
A ring has been found around Haumea, a world more than 2 billion kilometres beyond Pluto. The ring is the most distant ever seen in our solar system.

“This is a landmark discovery,” says Alan Stern at the Southwest Research Institute in Boulder, Colorado. “It’s very exciting.”

Until recently, the only known rings circled giant planets such as Saturn. In 2013, however, astronomers found two rings around Chariklo, an odd little rock about 250 kilometres across between the orbits of Saturn and Uranus. Chiron, one of Chariklo’s neighbours, may also have a ring.

Quote
Ortiz and Santos-Sanz also found that Haumea is slightly larger than once thought: at its widest, it is nearly the diameter of Pluto, the largest-known object orbiting the sun beyond Neptune. It is, however, only about 1025 kilometres across at its narrowest point, less than half Pluto’s diameter.

It is also much less dense than previously thought and has a make-up similar to Pluto’s. Both worlds are mostly rock, surrounded by water ice. And both are shiny, reflecting about half the light that strikes them.

https://www.newscientist.com/article/2150152-distant-dwarf-planet-near-pluto-has-a-ring-that-no-one-expected/amp/

More here.

http://www.iaa.es/en/news/haumea-most-peculiar-pluto-companions-has-ring-around-it
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/17/2017 07:17 PM
How Bright is the Moon, Really?

Quote
The “inconstant moon,” as Shakespeare called it in Romeo and Juliet, is more reliable than his pair of star-crossed lovers might have thought. Now researchers at the National Institute of Standards and Technology (NIST) plan to make the Moon even more reliable with a new project to measure its brightness.
Scientists put the Moon to work daily as a calibration source for space-based cameras that use the brightness and colors of sunlight reflecting off our planet to track weather patterns, trends in crop health, the locations of harmful algal blooms in oceans and much more. The information sent from Earth-facing imagers allows researchers to predict famines and floods and can help communities plan emergency response and disaster relief.
To make sure that one satellite camera’s “green” isn’t another’s “yellow,” each camera is calibrated—in space—against a common source. The Moon makes a convenient target because, unlike Earth, it has no atmosphere and its surface changes very little.
The trouble is that, for all the songs written about the light of the silvery Moon, it’s still not understood exactly how bright the Moon’s reflected light is, at all times and from all angles. Today’s best measurements allow researchers to calculate the Moon’s brightness with uncertainties of a few percent—not quite good enough for the most sensitive measurement needs, says NIST’s Stephen Maxwell. To make up for these shortcomings, scientists have developed complicated workarounds. For example, they must periodically check the accuracy of their satellite images by making the same measurements multiple ways—from space, from the air and from the ground—simultaneously.
Or, if they want to compare images taken at different times by different satellites, they have to ensure that there is some overlap during their time in space so that the imagers have the chance to measure the same part of the planet at roughly the same time. But what happens if a research team can’t get a new camera into space before an old one is retired? “You get what’s called a data gap, and you lose the ability to stitch together measurements from different satellites to determine long-term trends,” Maxwell says.
Really knowing how bright the Moon is—with uncertainties of much less than 1 percent—would reduce the need for these logistically challenging solutions and ultimately save money.
So NIST is setting out to take new measurements of the Moon’s brightness. Researchers hope they will be the best measurements to date.

https://www.nist.gov/news-events/news/2017/10/how-bright-moon-really
Title: Re: Exoplanets And Stars Thread
Post by: JasonAW3 on 10/17/2017 08:17 PM
Distant dwarf planet near Pluto has a ring that no one expected

Quote
A ring has been found around Haumea, a world more than 2 billion kilometres beyond Pluto. The ring is the most distant ever seen in our solar system.

“This is a landmark discovery,” says Alan Stern at the Southwest Research Institute in Boulder, Colorado. “It’s very exciting.”

Until recently, the only known rings circled giant planets such as Saturn. In 2013, however, astronomers found two rings around Chariklo, an odd little rock about 250 kilometres across between the orbits of Saturn and Uranus. Chiron, one of Chariklo’s neighbours, may also have a ring.

Quote
Ortiz and Santos-Sanz also found that Haumea is slightly larger than once thought: at its widest, it is nearly the diameter of Pluto, the largest-known object orbiting the sun beyond Neptune. It is, however, only about 1025 kilometres across at its narrowest point, less than half Pluto’s diameter.

It is also much less dense than previously thought and has a make-up similar to Pluto’s. Both worlds are mostly rock, surrounded by water ice. And both are shiny, reflecting about half the light that strikes them.

https://www.newscientist.com/article/2150152-distant-dwarf-planet-near-pluto-has-a-ring-that-no-one-expected/amp/

More here.

http://www.iaa.es/en/news/haumea-most-peculiar-pluto-companions-has-ring-around-it

It occurs to me to wonder whether or not Huemea may be a fast rotating low density object.

It could be that the ring is ice that was flung off of the surface of Huemea, during it's "spin-up".  This could have been induced from a glancing strike by a high velocity object impacting its' surface at an angle.

Otherwise, it might have once been a spherical object, prior to the impact, even allowing for it's low density.
Title: Re: Exoplanets And Stars Thread
Post by: hop on 10/18/2017 03:38 AM
A follow up on the Teachey and Kipping exomoon candidate discussed earlier (http://forum.nasaspaceflight.com/index.php?topic=42108.msg1707055#msg1707055).

The nature of the giant exomoon candidate Kepler-1625 b-i (https://arxiv.org/abs/1710.06209) René Heller

(note, submitted not yet reviewed)

Quote
The recent announcement of a Neptune-sized exomoon candidate around the transiting Jupiter-sized object Kepler-1625 b could indicate the presence of a hitherto unknown kind of gas giant moons, if confirmed. Three transits have been observed, allowing radius estimates of both objects. Here we investigate possible mass regimes of the transiting system that could produce the observed signatures and study them in the context of moon formation in the solar system, i.e. via impacts, capture, or in-situ accretion. The radius of Kepler-1625 b suggests it could be anything from a gas giant planet somewhat more massive than Saturn (0.4 M_Jup) to a brown dwarf (BD) (up to 75 M_Jup) or even a very-low-mass star (VLMS) (112 M_Jup ~ 0.11 M_sun). The proposed companion would certainly have a planetary mass. Possible extreme scenarios range from a highly inflated Earth-mass gas satellite to an atmosphere-free water-rock companion of about 180 M_Ear. Furthermore, the planet-moon dynamics during the transits suggest a total system mass of 17.6_{-12.6}^{+19.2} M_Jup. A Neptune-mass exomoon around a giant planet or low-mass BD would not be compatible with the common mass scaling relation of the solar system moons about gas giants. The case of a mini-Neptune around a high-mass BD or a VLMS, however, would be located in a similar region of the satellite-to-host mass ratio diagram as Proxima b, the TRAPPIST-1 system, and LHS 1140 b. The capture of a Neptune-mass object around a 10 M_Jup planet during a close binary encounter is possible in principle. The ejected object, however, would have had to be a super-Earth object, raising further questions of how such a system could have formed. In summary, this exomoon candidate is barely compatible with established moon formation theories. If it can be validated as orbiting a super-Jovian planet, then it would pose an exquisite riddle for formation theorists to solve.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/20/2017 06:09 PM
NOPE, OUR TEMPORARY MOON ISN’T SPACE JUNK, IT’S AN ASTEROID

https://www.universetoday.com/137564/nope-temporary-moon-isnt-space-junk-asteroid/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/23/2017 05:05 PM
The proton and the antiproton are basically identical — indicating that maybe, the universe shouldn’t exist

https://www.zmescience.com/science/physics/proton-antimatter-magnetic-moment-23102017/
Title: Re: Exoplanets And Stars Thread
Post by: JasonAW3 on 10/23/2017 07:12 PM
The proton and the antiproton are basically identical — indicating that maybe, the universe shouldn’t exist

https://www.zmescience.com/science/physics/proton-antimatter-magnetic-moment-23102017/

Interesting question;  Is it possible that what we commonly refer to as "anti-matter" could exist as a non-baryonic form often referred to as Dark Matter?

If an equal mass of anti-matter were somehow "out of-phase", or more precisely, partially separated from this universe on a separate partial Brane, allowing the mass influences without the direct interaction of matter and anti-matter, would this not account for the absence of anti-matter, Dark Matter itself,  and part of the "missing mass" that appears absent in our universe?
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/24/2017 03:41 PM
Spots On Supergiant Star Drive Spirals In Stellar Wind

https://scienmag.com/spots-on-supergiant-star-drive-spirals-in-stellar-wind/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/24/2017 07:25 PM
The nature of the giant exomoon candidate Kepler-1625 b-i

Quote
The recent announcement of a Neptune-sized exomoon candidate around the transiting Jupiter-sized object Kepler-1625 b could indicate the presence of a hitherto unknown kind of gas giant moons, if confirmed. Three transits have been observed, allowing radius estimates of both objects. Here we investigate possible mass regimes of the transiting system that could produce the observed signatures and study them in the context of moon formation in the solar system, i.e. via impacts, capture, or in-situ accretion. The radius of Kepler-1625 b suggests it could be anything from a gas giant planet somewhat more massive than Saturn (0.4 M_Jup) to a brown dwarf (BD) (up to 75 M_Jup) or even a very-low-mass star (VLMS) (112 M_Jup ~ 0.11 M_sun). The proposed companion would certainly have a planetary mass. Possible extreme scenarios range from a highly inflated Earth-mass gas satellite to an atmosphere-free water-rock companion of about 180 M_Ear. Furthermore, the planet-moon dynamics during the transits suggest a total system mass of 17.6_{-12.6}^{+19.2} M_Jup. A Neptune-mass exomoon around a giant planet or low-mass BD would not be compatible with the common mass scaling relation of the solar system moons about gas giants. The case of a mini-Neptune around a high-mass BD or a VLMS, however, would be located in a similar region of the satellite-to-host mass ratio diagram as Proxima b, the TRAPPIST-1 system, and LHS 1140 b. The capture of a Neptune-mass object around a 10 M_Jup planet during a close binary encounter is possible in principle. The ejected object, however, would have had to be a super-Earth object, raising further questions of how such a system could have formed. In summary, this exomoon candidate is barely compatible with established moon formation theories. If it can be validated as orbiting a super-Jovian planet, then it would pose an exquisite riddle for formation theorists to solve.

https://arxiv.org/abs/1710.06209
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/25/2017 07:31 PM
New article.

Project Blue and the quest to photograph exoplanets

https://phys.org/news/2017-10-blue-quest-exoplanets.amp
Post by: Star One on 10/26/2017 07:24 PM
Astronomers discover sunscreen snow falling on hot exoplanet

Quote
Astronomers at Penn State have used the Hubble Space Telescope to find a blistering-hot giant planet outside our solar system where the atmosphere "snows" titanium dioxide -- the active ingredient in sunscreen. These Hubble observations are the first detections of this "snow-out" process, called a "cold trap," on an exoplanet. This discovery, and other observations made by the Penn State team, provide insight into the complexity of weather and atmospheric composition on exoplanets, and may someday be useful for gauging the habitability of Earth-size planets.

http://science.psu.edu/news-and-events/2017-news/Beatty10-2017
Post by: Star One on 10/31/2017 04:46 PM
Scientists detect comets outside our solar system

Quote
Scientists from MIT and other institutions, working closely with amateur astronomers, have spotted the dusty tails of six exocomets — comets outside our solar system — orbiting a faint star 800 light years from Earth.
These cosmic balls of ice and dust, which were about the size of Halley’s Comet and traveled about 100,000 miles per hour before they ultimately vaporized, are some of the smallest objects yet found outside our own solar system.
The discovery marks the first time that an object as small as a comet has been detected using transit photometry, a technique by which astronomers observe a star’s light for telltale dips in intensity. Such dips signal potential transits, or crossings of planets or other objects in front of a star, which momentarily block a small fraction of its light.
In the case of this new detection, the researchers were able to pick out the comet’s tail, or trail of gas and dust, which blocked about one-tenth of 1 percent of the star’s light as the comet streaked by.

http://news.mit.edu/2017/scientists-detect-comets-outside-our-solar-system-1026

We may have found 20 habitable worlds hiding in plain sight

Quote
There could be more habitable planets out there than we thought. An analysis of data from the Kepler space telescope has revealed 20 promising worlds that might be able to host life.

The list of potential worlds includes several planets that orbit stars like our sun. Some take a relatively long time to complete a single orbit, with the longest taking 395 Earth days and others taking Earth weeks or months. The fastest orbit is 18 Earth days. This is very different to the very short “years” we see around smaller stars with habitable planets like Proxima Centauri.

The exoplanet with a 395-day year is one of the most promising worlds for life on the list, says Jeff Coughlin, a Kepler team lead who helped find the potential planets. Called KOI-7923.01, it is 97 per cent the size of Earth, but a little colder.

Its cooler temperature is due to its distance from its star and the fact that the star is slightly cooler than our sun. This means it may be a little more like tundra regions on Earth than temperate ones, but is still warm enough and large enough to hold the liquid water essential to life as we know it.

“If you had to choose one to send a spacecraft to, it’s not a bad option,” says Coughlin.

A solid chance
The team is 70 to 80 per cent certain that these are solid candidates, he says. They can’t be confirmed yet as more observations are needed: the planets all come from the original Kepler mission, which stared at the same region of the sky for only four years before its aiming ability was crippled when its reaction wheels broke in 2013. This means that we have only seen each of these planets once or twice due to their long orbits, and the signals could be a little wobbly.

Ground-based observatories or the Hubble Space Telescope will have to take more observations over the coming years to double-check, Coughlin says.

https://www.newscientist.com/article/may-found-20-habitable-worlds-hiding-plain-sight/

Here’s the paper.

https://arxiv.org/abs/1710.06758
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 10/31/2017 07:59 PM
Exoplanet-Hunting Survey Discovers Three More Giant Alien Worlds!

Quote
From the SuperWASP survey data, Dr. Demangeon and her colleagues were able to detect three transit signals coming from three distant stars – WASP-151, WASP-153 and WASP-156. This was then followed by spectroscopic observations performed using the Haute-Provence Observatory in France and the La Silla Observatory in Chile, which allowed the team to confirm the nature of these planets.

From this, they determined that WASP-151b and WASP-153b are two “hot Saturns”, meaning they are low-density gas giants with close orbits. They orbit their respective suns, which are both early G-type stars (aka. yellow dwarfs, like our Sun), with an orbital period of 4.53 and 3.33 days. WASP-156b, meanwhile, is a Super-Neptune that orbits a K-type (orange dwarf) star.

Quote
Taken together, these planets represent some major opportunities for exoplanet research. As they indicate, “these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert.” This refers to the boundary astronomers have observed around stars where shot period Neptune-size planets are very unlikely to be found.

Quote
The team also offered some possible explanations for the existence of a “Neptunian desert” based on their findings. For starters, they proposed that a high-eccentricity migration could be responsible, where Neptune-sized ice giants form in the outer reaches of a star system and migrate inward over time. They also indicate that their discovery offers compelling evidence that ultra-violet radiation and gas envelope-depletion could be a key part of the puzzle.

https://www.universetoday.com/137671/exoplanet-hunting-survey-discovers-three-giant-alien-worlds/amp/
Title: Re: Exoplanets And Stars Thread
Post by: jebbo on 11/01/2017 06:40 AM
First planet for the "Next Generation Transit Survey" programme.

Quote
We present the discovery of NGTS-1b, a hot-Jupiter transiting an early M-dwarf host (Teff=3916+71−63 K) in a P=2.674d orbit discovered as part of the Next Generation Transit Survey (NGTS). The planet has a mass of 0.812+0.066−0.075 MJ, making it the most massive planet ever discovered transiting an M-dwarf. The radius of the planet is 1.33+0.61−0.33 RJ. Since the transit is grazing, we determine this radius by modelling the data and placing a prior on the density from the population of known gas giant planets. NGTS-1b is the third transiting giant planet found around an M-dwarf, reinforcing the notion that close-in gas giants can form and migrate similar to the known population of hot Jupiters around solar type stars. The host star shows no signs of activity, and the kinematics hint at the star being from the thick disk population. With a deep (2.5%) transit around a K=11.9 host, NGTS-1b will be a strong candidate to probe giant planet composition around M-dwarfs via JWST transmission spectroscopy.

https://arxiv.org/abs/1710.11099 (https://arxiv.org/abs/1710.11099)
https://arxiv.org/abs/1710.11100 (https://arxiv.org/abs/1710.11100)

Edit: worth noting that this planet puts the cat slightly amongst the planet-formation pigeons as planets this large were not expected around such small stars.

--- Tony
Post by: Star One on 11/01/2017 11:56 AM
First planet for the "Next Generation Transit Survey" programme.

Quote
We present the discovery of NGTS-1b, a hot-Jupiter transiting an early M-dwarf host (Teff=3916+71−63 K) in a P=2.674d orbit discovered as part of the Next Generation Transit Survey (NGTS). The planet has a mass of 0.812+0.066−0.075 MJ, making it the most massive planet ever discovered transiting an M-dwarf. The radius of the planet is 1.33+0.61−0.33 RJ. Since the transit is grazing, we determine this radius by modelling the data and placing a prior on the density from the population of known gas giant planets. NGTS-1b is the third transiting giant planet found around an M-dwarf, reinforcing the notion that close-in gas giants can form and migrate similar to the known population of hot Jupiters around solar type stars. The host star shows no signs of activity, and the kinematics hint at the star being from the thick disk population. With a deep (2.5%) transit around a K=11.9 host, NGTS-1b will be a strong candidate to probe giant planet composition around M-dwarfs via JWST transmission spectroscopy.

https://arxiv.org/abs/1710.11099 (https://arxiv.org/abs/1710.11099)
https://arxiv.org/abs/1710.11100 (https://arxiv.org/abs/1710.11100)

Edit: worth noting that this planet puts the cat slightly amongst the planet-formation pigeons as planets this large were not expected around such small stars.

--- Tony

Wouldn’t one answer by that this was a wandering planet that was captured by this star?
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 11/01/2017 11:05 PM
Edit: worth noting that this planet puts the cat slightly amongst the planet-formation pigeons as planets this large were not expected around such small stars.

Wouldn’t one answer by that this was a wandering planet that was captured by this star?

It is an answer, but an extremely unlikely one. Not only would such a rogue planet have to come sufficiently near the star - and space is big compared to stars - but capture is not a straightforward process (generally there needs to be a third body of comparable size involved).

An alternative explanation is that this object was formed at the same time as its host star by direct collapse of the nebula - i.e. it's a very small brown dwarf (sub-brown dwarf?). I'm not sure if there are any theoretical minimums for the mass of objects formed by such a mechanism!
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 11/02/2017 10:44 AM
Edit: worth noting that this planet puts the cat slightly amongst the planet-formation pigeons as planets this large were not expected around such small stars.

Wouldn’t one answer by that this was a wandering planet that was captured by this star?

It is an answer, but an extremely unlikely one. Not only would such a rogue planet have to come sufficiently near the star - and space is big compared to stars - but capture is not a straightforward process (generally there needs to be a third body of comparable size involved).

An alternative explanation is that this object was formed at the same time as its host star by direct collapse of the nebula - i.e. it's a very small brown dwarf (sub-brown dwarf?). I'm not sure if there are any theoretical minimums for the mass of objects formed by such a mechanism!

The mass estimates put below the minimum for a Brown Dwarf.
Title: Re: Exoplanets And Stars Thread
Post by: clongton on 11/02/2017 03:42 PM
Edit: worth noting that this planet puts the cat slightly amongst the planet-formation pigeons as planets this large were not expected around such small stars.

Wouldn’t one answer by that this was a wandering planet that was captured by this star?

It is an answer, but an extremely unlikely one. Not only would such a rogue planet have to come sufficiently near the star - and space is big compared to stars - but capture is not a straightforward process (generally there needs to be a third body of comparable size involved).

An alternative explanation is that this object was formed at the same time as its host star by direct collapse of the nebula - i.e. it's a very small brown dwarf (sub-brown dwarf?). I'm not sure if there are any theoretical minimums for the mass of objects formed by such a mechanism!

The mass estimates put below the minimum for a Brown Dwarf.

The minimum is a yet unproven theorem that may or may not be correct. The more we learn the faster our precious theorems fall by the wayside. It may ultimately prove to be correct but it will be a long, long time before that can occur. Best not to dismiss an idea based on unproven theorems.
Title: Re: Exoplanets And Stars Thread
Post by: jebbo on 11/02/2017 06:01 PM
For a bit of fun, follow the #ExoCup tag on Twitter ... interesting to see the advocacy for people's favourite exoplanets.

And it is actually fun!

--- Tony
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 11/03/2017 04:36 PM
ALMA Discovery of Dust Belts Around Proxima Centauri

Quote
Proxima Centauri, the star closest to our Sun, is known to host at least one terrestrial planet candidate in a temperate orbit. Here we report the ALMA detection of the star at 1.3 mm wavelength and the discovery of a belt of dust orbiting around it at distances ranging between 1 and 4 au, approximately. Given the low luminosity of the Proxima Centauri star, we estimate a characteristic temperature of about 40 K for this dust, which might constitute the dust component of a small-scale analog to our solar system Kuiper belt. The estimated total mass, including dust and bodies up to 50 km in size, is of the order of 0.01 Earth masses, which is similar to that of the solar Kuiper belt. Our data also show a hint of warmer dust closer to the star. We also find signs of two additional features that might be associated with the Proxima Centauri system, which, however, still require further observations to be confirmed: an outer extremely cold (about 10 K) belt around the star at about 30 au, whose orbital plane is tilted about 45 degrees with respect to the plane of the sky; and additionally, we marginally detect a compact 1.3 mm emission source at a projected distance of about 1.2 arcsec from the star, whose nature is still unknown.

https://arxiv.org/abs/1711.00578
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 11/03/2017 10:59 PM
An alternative explanation is that this object was formed at the same time as its host star by direct collapse of the nebula - i.e. it's a very small brown dwarf (sub-brown dwarf?). I'm not sure if there are any theoretical minimums for the mass of objects formed by such a mechanism!

The mass estimates put below the minimum for a Brown Dwarf.

The minimum is a yet unproven theorem that may or may not be correct. The more we learn the faster our precious theorems fall by the wayside. It may ultimately prove to be correct but it will be a long, long time before that can occur. Best not to dismiss an idea based on unproven theorems.

The definition of a brown dwarf appears to still be subject to debate. Some define it as a sub-stellar object that is massive enough (>~13Mj) to undergo deuterium fusion. On that definition, this object is not a brown dwarf. Others define it as a sub-stellar object that was formed by the collapse of a nebula. I'm not aware of the minimum size of such objects (if any, though gas pressure presumably would overcome gravitational forces at some point?). By that definition this could be a brown dwarf. Given the definitional conflict I tentatively suggested the term 'sub-brown dwarf'! :)

ALMA Discovery of Dust Belts Around Proxima Centauri

I found the tentative possibility of a Saturn analogue (rings and all) to be the most interesting aspect:

Quote
Finally, an exciting alternative scenario is that the source traces a ring of dust surrounding an as yet undiscovered giant planet orbiting at a (projected) distance of 1.6 au (orbital period >~5.8 yr). ... we would expect a planet of mass ∼100 M⊕, the mass of Saturn, to account for the observed 1.3 mm emission. No clear RV signal that would indicate such a planet is present in the data of the long-term monitoring of the star. Further observations are being undertaken to confirm, or rule out this intriguing possibility. At any rate, our study shows that ALMA provides already the necessary sensitivity and resolution to detect rings around exoplanets in alpha Centauri, and perhaps in other nearby stars.
Post by: Star One on 11/03/2017 11:01 PM
An alternative explanation is that this object was formed at the same time as its host star by direct collapse of the nebula - i.e. it's a very small brown dwarf (sub-brown dwarf?). I'm not sure if there are any theoretical minimums for the mass of objects formed by such a mechanism!

The mass estimates put below the minimum for a Brown Dwarf.

The minimum is a yet unproven theorem that may or may not be correct. The more we learn the faster our precious theorems fall by the wayside. It may ultimately prove to be correct but it will be a long, long time before that can occur. Best not to dismiss an idea based on unproven theorems.

The definition of a brown dwarf appears to still be subject to debate. Some define it as a sub-stellar object that is massive enough (>~13Mj) to undergo deuterium fusion. On that definition, this object is not a brown dwarf. Others define it as a sub-stellar object that was formed by the collapse of a nebula. I'm not aware of the minimum size of such objects (if any, though gas pressure presumably would overcome gravitational forces at some point?). By that definition this could be a brown dwarf. Given the definitional conflict I tentatively suggested the term 'sub-brown dwarf'!

ALMA Discovery of Dust Belts Around Proxima Centauri

I found the tentative possibility of a Saturn analogue (rings and all) to be the most interesting aspect:

Quote
Finally, an exciting alternative scenario is that the source traces a ring of dust surrounding an as yet undiscovered giant planet orbiting at a (projected) distance of 1.6 au (orbital period >~5.8 yr). ... we would expect a planet of mass ∼100 M⊕, the mass of Saturn, to account for the observed 1.3 mm emission. No clear RV signal that would indicate such a planet is present in the data of the long-term monitoring of the star. Further observations are being undertaken to confirm, or rule out this intriguing possibility. At any rate, our study shows that ALMA provides already the necessary sensitivity and resolution to detect rings around exoplanets in alpha Centauri, and perhaps in other nearby stars.

If it is anywhere near as big as Saturn that’s another small star with an extremely big planet.

This link posted in the Red Dot thread seems to suggest it isn’t a gas giant.

http://www.astronomy.com/news/2017/11/proxima-rings
Title: Re: Exoplanets And Stars Thread
Post by: Alpha_Centauri on 11/03/2017 11:11 PM
Except the current RV surveys even before the most recent observations have already ruled out such a massive planet at this distance.
Title: Re: Exoplanets And Stars Thread
Post by: Bynaus on 11/04/2017 04:24 PM
The mass of the planet has only been guestimated from a ring-mass-to-planet-mass ratio of 1e-7. Whether it really is a ring, or whether planets with larger mass ratios exist are open questions.

"More work is necessary".
Title: Re: Exoplanets And Stars Thread
Post by: CuddlyRocket on 11/04/2017 07:05 PM
Except the current RV surveys even before the most recent observations have already ruled out such a massive planet at this distance.

Quoting from the paper:
Quote
No clear RV signal that would indicate such a planet is present in the data of the long-term monitoring of the star. Further observations are being undertaken to confirm, or rule out this intriguing possibility.

So, according to them, it's still an open question.
Title: Re: Exoplanets And Stars Thread
Post by: Dao Angkan on 11/06/2017 06:03 PM
Edit: worth noting that this planet puts the cat slightly amongst the planet-formation pigeons as planets this large were not expected around such small stars.

Wouldn’t one answer by that this was a wandering planet that was captured by this star?

It is an answer, but an extremely unlikely one. Not only would such a rogue planet have to come sufficiently near the star - and space is big compared to stars - but capture is not a straightforward process (generally there needs to be a third body of comparable size involved).

An alternative explanation is that this object was formed at the same time as its host star by direct collapse of the nebula - i.e. it's a very small brown dwarf (sub-brown dwarf?). I'm not sure if there are any theoretical minimums for the mass of objects formed by such a mechanism!

According to Shiv S. Kumar (who first theorised Brown Dwarfs in the 1960s) the theoretical minimum mass from cloud collapse is supposedly ~1 MJup, which is close to the mass range for this body (although slightly higher). Incidentally, the theoretical maximum mass from core accretion  in the vicinity of a star of any mass is supposedly ~2 MJup, presumably lower for low mass stars. This object is pretty close to the ~1 MJup limit, so may just be massive enough to have formed by cloud collapse.

The Bottom of the Main Sequence and Beyond: Speculations, Calculations, Observations, and Discoveries (1958-2002) (https://www.cambridge.org/core/services/aop-cambridge-core/content/view/01E697652BC3A1F68E814D1EBF8A6D85/S0074180900210176a.pdf/bottom_of_the_main_sequence_and_beyond_speculations_calculations_observations_and_discoveries_19582002.pdf)

Quote
The Basic Nature of the Stars and Planets

Since  1964,  I  have been presenting arguments to  show that the star formation processes are fundamentally different from those of planet formation (Kumar 1964; Kumar 1967; Kumar 1972a; Kumar 1974; Kumar 1990; Kumar 1995; Kumar 2000a). Stars (including brown dwarfs) are formed by the fragmentation of gaseous clouds, and the mass range in the stellar domain ranges from  a  few hundred solar masses to ~0.001 M☉ (or  ~1 MJup). Planets are formed by the slow accumulation (accretion) of dust, rocks, and gas  in the vicinity of  a star, and the mass range in the planetary domain ranges from ~0.000001 MJup to  ~2 MJup. Thus, as  far  as the masses of the stars and planets are concerned, I'm not talking of just one linear sequence but of  two separate sequences arising from two different formation processes.

The old idea that the stars and planets represent two sections of the same linear sequence (in mass), with objects above a certain mass labeled as stars and objects below that certain mass labeled as planets, is not the correct way  to understand the two groups of objects. The mass of  an object doesn't uniquely determine its basic nature. In order to ascertain the basic nature of an object, we have  to  know its formation mechanism. Theoretically speaking, an object of  1MJup (located somewhere in the Universe) may come into existence by either the star formation processes or the planet formation processes. As I have repeatedly pointed out (Kumar 1972a; Kumar 1974; Kumar 1994; Kumar 1995), the most massive planet in the Solar System (Jupiter) was most probably formed by the planet formation processes and not by the star formation processes. For Jupiter, the presence of  a rocky/metallic core, the chemical composition of its interior, and the chemical compositin of its atmosphere clearly indicate that the planet acquired its present mass  (in the presence of the Sun)  by the slow accretion of dust, rocks, and gas  over the past 4.5  billion years (Kumar 1994; Kumar 1995; Kumar 2000a).  It  does not appear to have been formed by the rapid collapse of an extended, gaseous object of mass  0.001 M☉.
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 11/06/2017 07:15 PM
NuSTAR probes black hole mystery

Quote
Black holes are famous for being ravenous eaters, but they do not eat everything that falls toward them. A small portion of material gets shot back out in powerful jets of hot gas, called plasma, that can wreak havoc on their surroundings. Along the way, this plasma somehow gets energized enough to strongly radiate light, forming two bright columns along the black hole’s axis of rotation. Scientists have long debated where and how this happens in the jet.

Astronomers have new clues to this mystery. Using NASA’s NuSTAR space telescope and a fast camera called ULTRACAM on the William Herschel Observatory in La Palma, Spain, scientists have been able to measure the distance that particles in jets travel before they “turn on” and become bright sources of light. This distance is called the “acceleration zone.” The study is published in the journal Nature Astronomy.

https://astronomynow.com/2017/11/05/nustar-probes-black-hole-mystery/
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 11/07/2017 08:17 PM
Alma’s image of red giant star gives a surprising glimpse of the Sun’s future

Quote
A Chalmers-led team of astronomers has for the first time observed details on the surface of an aging star with the same mass as the Sun. ALMA:s images show that the star is a giant, its diameter twice the size of Earth’s orbit around the Sun, but also that the star’s atmosphere is affected by powerful, unexpected shock waves. The research is published in Nature Astronomy on 30 October 2017.

http://www.chalmers.se/en/researchinfrastructure/oso/news/Pages/Alma-image-of-red-giant-star-gives-a-surprising-glimpse-of-the-Suns-future.aspx
Title: Re: Exoplanets And Stars Thread
Post by: Star One on 11/08/2017 07:48 PM
MSU biologists have found out how long can microorganisms live on Mars

Quote
"The results of the study indicate the possibility of prolonged cryoconservation of viable microorganisms in the Martian regolith. The intensity of ionizing radiation on the surface of Mars is 0.05-0.076 Gy/year and decreases with depth. Taking into account the intensity of radiation in the Mars regolith, the data obtained by us makes it possible to assume that hypothetical Mars ecosystems could be conserved in anabiotic state in the surface layer of regolith (protected from UV rays) for at least 1.3-2 million years, at a depth of two meters for no less than 3.3 million years, and at a depth of five meters for at least 20 million years. The data obtained can also be applied to assess the possibility of detecting viable microorganisms at other objects of the Solar System and within small bodies in outer space" - the scientist added.

The authors have for the first time proven that prokaryotes can survive irradiation with ionizing radiation in doses exceeding 80 kGy. The data obtained indicate both a possible underestimation of the radiation resistance of natural microbial communities and the need to study the joint effect of a set of extraterrestrial and cosmic factors on living organisms and biomolecules in astrobiological model experiments.

Post by: Star One on 11/10/2017 06:36 AM
OGLE-2016-BLG-1190Lb: First Spitzer Bulge Planet Lies Near the Planet/Brown-Dwarf Boundary

Quote
We report the discovery of OGLE-2016-BLG-1190Lb, which is likely to be the first Spitzer microlensing planet in the Galactic bulge/bar, an assignation that can be confirmed by two epochs of high-resolution imaging of the combined source-lens baseline object. The planet's mass M_p= 13.4+-0.9 M_J places it right at the deuterium burning limit, i.e., the conventional boundary between "planets" and "brown dwarfs". Its existence raises the question of whether such objects are really "planets" (formed within the disks of their hosts) or "failed stars" (low mass objects formed by gas fragmentation). This question may ultimately be addressed by comparing disk and bulge/bar planets, which is a goal of the Spitzer microlens program. The host is a G dwarf M_host = 0.89+-0.07 M_sun and the planet has a semi-major axis a~2.0 AU. We use Kepler K2 Campaign 9 microlensing data to break the lens-mass degeneracy that generically impacts parallax solutions from Earth-Spitzer observations alone, which is the first successful application of this approach. The microlensing data, derived primarily from near-continuous, ultra-dense survey observations from OGLE, MOA, and three KMTNet telescopes, contain more orbital information than for any previous microlensing planet, but not quite enough to accurately specify the full orbit. However, these data do permit the first rigorous test of microlensing orbital-motion measurements, which are typically derived from data taken over <1% of an orbital period.

https://arxiv.org/abs/1710.09974
Post by: Star One on 11/15/2017 05:04 PM
Ross 128 b: A ‘Temperate’ Planet?

Quote
What gives the Ross 128 b detection a wrinkle of astrobiological interest is that the star the planet orbits is relatively inactive. Red dwarfs are known for the flares that can flood nearby planets with ultraviolet and X-ray radiation. Compounded with the fact that habitable zone planets must orbit quite close to a parent M-dwarf (given the star’s small size and low temperature compared to the Sun), such flares could act as a brake on the development of life.

Ross 128 b may thus have a higher likelihood for astrobiological activity than Proxima b, assuming that it actually is in the habitable zone. Right now the team behind this work, led by Xavier Bonfils (Université Grenoble Alpes) hedges its bets by referring to the planet as ‘temperate’ and ‘close to the inner edge of the conventional habitable zone.’

https://www.centauri-dreams.org/?p=38800
Post by: CuddlyRocket on 11/16/2017 05:16 AM
Ross 128 b: A ‘Temperate’ Planet?

You can find the paper at A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs (https://www.eso.org/public/archives/releases/sciencepapers/eso1736/eso1736a.pdf)

Quote
(from the abstract) Here we report on our radial velocity observations of Ross 128 (Proxima Virginis, GJ447, HIP 57548), an M4 dwarf just 3.4 parsec away from our Sun. This source hosts an exo-Earth with a projected mass m sin i = 1.35M⊕ and an orbital period of 9.9 days. Ross 128 b receives ∼1.38 times as much flux as Earth from the Sun and its equilibrium ranges in temperature between 269 K for an Earth-like albedo and 213 K for a Venus-like albedo. Recent studies place it close to the inner edge of the conventional habitable zone. An 80-day long light curve from K2 campaign C01 demonstrates that Ross 128 b does not transit. Together with the All Sky Automated Survey (ASAS) photometry and spectroscopic activity indices, the K2 photometry shows that Ross 128 rotates slowly and has weak magnetic activity. In a habitability context, this makes survival of its atmosphere against erosion more likely. Ross 128 b is the second closest known exo-Earth, after Proxima Centauri b (1.3 parsec), and the closest temperate planet known around a quiet star.

Interesting the use of the Kepler K2 data. Not gone unnoticed by the latter :) :

NASA's Kepler/K2 GO Office‏ @KeplerGO
8 hours ago
Did you know?  @NASAKepler observed #Ross128b in 2014!  The discovery paper uses these Kepler data to show that the planet does not transit, and that the host star is magnetically quiet and rotating slowly.  @ESO's #HARPS and @NASA's #K2Mission are a winning combo!
Post by: Star One on 11/16/2017 05:51 AM
Ross 128 b: A ‘Temperate’ Planet?

You can find the paper at A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs (https://www.eso.org/public/archives/releases/sciencepapers/eso1736/eso1736a.pdf)

Quote
(from the abstract) Here we report on our radial velocity observations of Ross 128 (Proxima Virginis, GJ447, HIP 57548), an M4 dwarf just 3.4 parsec away from our Sun. This source hosts an exo-Earth with a projected mass m sin i = 1.35M⊕ and an orbital period of 9.9 days. Ross 128 b receives ∼1.38 times as much flux as Earth from the Sun and its equilibrium ranges in temperature between 269 K for an Earth-like albedo and 213 K for a Venus-like albedo. Recent studies place it close to the inner edge of the conventional habitable zone. An 80-day long light curve from K2 campaign C01 demonstrates that Ross 128 b does not transit. Together with the All Sky Automated Survey (ASAS) photometry and spectroscopic activity indices, the K2 photometry shows that Ross 128 rotates slowly and has weak magnetic activity. In a habitability context, this makes survival of its atmosphere against erosion more likely. Ross 128 b is the second closest known exo-Earth, after Proxima Centauri b (1.3 parsec), and the closest temperate planet known around a quiet star.

Interesting the use of the Kepler K2 data. Not gone unnoticed by the latter :) :

NASA's Kepler/K2 GO Office‏ @KeplerGO
8 hours ago
Did you know?  @NASAKepler observed #Ross128b in 2014!  The discovery paper uses these Kepler data to show that the planet does not transit, and that the host star is magnetically quiet and rotating slowly.  @ESO's #HARPS and @NASA's #K2Mission are a winning combo!

It’s frustrating that both this exoplanet & Proxima b do not transit their star’s from our prospective.
Post by: jebbo on 11/16/2017 07:22 AM
It’s frustrating that both this exoplanet & Proxima b do not transit their star’s from our prospective.

It certainly makes things harder, but both are very near so all is not lost:
* JWST should be able to get low resolution spectroscopy for Proxima b (good enough to detect CO2 and possibly O3).
* Direct imaging is very challenging due to the IWA and contrast requirements but there are various proposals that would manage it (free flying star shades etc)

--- Tony
Post by: Star One on 11/16/2017 07:23 AM
It’s frustrating that both this exoplanet & Proxima b do not transit their star’s from our prospective.

It certainly makes things harder, but both are very near so all is not lost:
* JWST should be able to get low resolution spectroscopy for Proxima b (good enough to detect CO2 and possibly O3).
* Direct imaging is very challenging due to the IWA and contrast requirements but there are various proposals that would manage it (free flying star shades etc)

--- Tony

Is one of them, even though neither transit, better positioned for observation than the other?
Post by: jebbo on 11/16/2017 07:37 AM
Is one of them, even though neither transit, better positioned for observation than the other?

Intuitively I'd say Proxima is easier, purely because it is closer (certainly helps with IWA)

Edit: with a bit of work (a few years), we could get spectra for Proxima b using the VLT.  It needs an upgrade to SPHERE (new coronagraph) and a new fibre feed from the Naysmith A focus to ESPRESSO but it sounds feasible (and fits ESO's strategy of testing instrument for new telescopes on the previous generation).
https://arxiv.org/abs/1609.03082 (https://arxiv.org/abs/1609.03082)

--- Tony
Post by: Star One on 11/16/2017 03:21 PM
Is one of them, even though neither transit, better positioned for observation than the other?

Intuitively I'd say Proxima is easier, purely because it is closer (certainly helps with IWA)

Edit: with a bit of work (a few years), we could get spectra for Proxima b using the VLT.  It needs an upgrade to SPHERE (new coronagraph) and a new fibre feed from the Naysmith A focus to ESPRESSO but it sounds feasible (and fits ESO's strategy of testing instrument for new telescopes on the previous generation).
https://arxiv.org/abs/1609.03082 (https://arxiv.org/abs/1609.03082)

--- Tony

Is Ross 128b just a bit to far then for these instruments?
Post by: jebbo on 11/16/2017 03:44 PM
Is Ross 128b just a bit to far then for these instruments?

Yes ... 2.5 times the distance, so smaller inner working angle (sin(IWA) is inversely proportional to distance). Proxima b is already right at the 2lambda/D limit for 750nm.

--- Tony
Post by: Star One on 11/16/2017 03:53 PM
Is Ross 128b just a bit to far then for these instruments?

Yes ... 2.5 times the distance, so smaller inner working angle (sin(IWA) is inversely proportional to distance). Proxima b is already right at the 2lambda/D limit for 750nm.

--- Tony

So even in the next decade Ross 128b will escape our grasp so to speak.
Post by: jebbo on 11/16/2017 03:55 PM
No, it's probably in range for the 30m class of telescopes.

--- Tony
Post by: Star One on 11/16/2017 04:46 PM
No, it's probably in range for the 30m class of telescopes.

--- Tony

That’s good news then.
Post by: Star One on 11/20/2017 04:23 PM
A Case for an Atmosphere on Super-Earth 55 Cancri e

Quote
One of the primary questions when characterizing Earth-sized and super-Earth-sized exoplanets is whether they have a substantial atmosphere like Earth and Venus or a bare-rock surface like Mercury. Phase curves of the planets in thermal emission provide clues to this question, because a substantial atmosphere would transport heat more efficiently than a bare-rock surface. Analyzing phase-curve photometric data around secondary eclipses has previously been used to study energy transport in the atmospheres of hot Jupiters. Here we use phase curve, Spitzer time-series photometry to study the thermal emission properties of the super-Earth exoplanet 55 Cancri e. We utilize a semianalytical framework to fit a physical model to the infrared photometric data at 4.5 μm. The model uses parameters of planetary properties including Bond albedo, heat redistribution efficiency (i.e., ratio between radiative timescale and advective timescale of the atmosphere), and the atmospheric greenhouse factor. The phase curve of 55 Cancri e is dominated by thermal emission with an eastward-shifted hotspot. We determine the heat redistribution efficiency to be ${1.47}_{-0.25}^{+0.30}$, which implies that the advective timescale is on the same order as the radiative timescale. This requirement cannot be met by the bare-rock planet scenario because heat transport by currents of molten lava would be too slow. The phase curve thus favors the scenario with a substantial atmosphere. Our constraints on the heat redistribution efficiency translate to an atmospheric pressure of ~1.4 bar. The Spitzer 4.5 μm band is thus a window into the deep atmosphere of the planet 55 Cancri e.

http://iopscience.iop.org/article/10.3847/1538-3881/aa9278
Post by: Star One on 11/20/2017 04:53 PM
Giant telescope’s mobile-phone ‘dead zones’ rile South African residents

Quote
Sensitive radio dishes of the Square Kilometre Array will affect phone reception — and could harm local economies, say farmers.

Post by: Star One on 11/20/2017 07:18 PM
Phil Plait debunks the latest moon hoax nonsense and despairs that even Newsweek reproduced these ridiculous claims.

Quote
And it denigrates science. It demeans one of the most amazing challenges humans have ever undertaken, one of the greatest accomplishments in our history.

Perhaps even worse, it's painful to see a magazine like Newsweek promulgate such nonsense. I'll note in the article the writer didn't seek out any expert advice, despite a dozen people who could be found easily using a Google search. I'm one of them, and it took me literally three minutes to figure out exactly what's what in this photo. So yeah, it's irritating (though I'll very grudgingly give Streetcap1 one small piece of credit: He at least links to the original image; most conspiracy theorists don't, which should ring very loud alarm bells).

If there's a lesson to be learned here, it's that this little episode shows how flawed humans can be, how easily we can be swayed by the flimsiest of claims. That is part of our nature… just as it's part of our nature to seek out truth, to investigate the unknown, and to explore it. And while critical thinking and judicious skepticism are harder to implement, and may not be part of our nature, I'll remind you that we invented science. We recognize that we can be fooled, and we created an entire field of thinking and investigation to minimize that issue.

And the beauty is, it works!

After all, for real and for sure, it sent us to the Moon.

http://www.syfy.com/syfywire/no-thats-not-a-stagehand-in-an-apollo-astronaut-photo
Post by: Star One on 11/28/2017 05:15 PM
Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars

Quote
Despite more than 20 years since the discovery of the first gas giant planet with an anomalously large radius, the mechanism for planet inflation remains unknown. Here, we report the discovery of K2-132b, an inflated gas giant planet found with the NASA K2 Mission, and a revised mass for another inflated planet, K2-97b. These planets orbit on ≈9 day orbits around host stars that recently evolved into red giants. We constrain the irradiation history of these planets using models constrained by asteroseismology and Keck/High Resolution Echelle Spectrometer spectroscopy and radial velocity measurements. We measure planet radii of 1.31 ± 0.11 R J and 1.30 ± 0.07 R J, respectively. These radii are typical for planets receiving the current irradiation, but not the former, zero age main-sequence irradiation of these planets. This suggests that the current sizes of these planets are directly correlated to their current irradiation. Our precise constraints of the masses and radii of the stars and planets in these systems allow us to constrain the planetary heating efficiency of both systems as $0.03{ \% }_{-0.02 \% }^{+0.03 \% }$. These results are consistent with a planet re-inflation scenario, but suggest that the efficiency of planet re-inflation may be lower than previously theorized. Finally, we discuss the agreement within 10% of the stellar masses and radii, and the planet masses, radii, and orbital periods of both systems, and speculate that this may be due to selection bias in searching for planets around evolved stars.

http://iopscience.iop.org/article/10.3847/1538-3881/aa932d
Post by: Star One on 11/30/2017 08:56 PM
Subsurface Exolife

Quote
We study the prospects for life on planets with subsurface oceans, and find that a wide range of planets can exist in diverse habitats with relatively thin ice envelopes. We quantify the energy sources available to these worlds, the rate of production of prebiotic compounds, and assess their potential for hosting biospheres. Life on these planets is likely to face challenges, which could be overcome through a combination of different mechanisms. We quantify the number of such worlds, and find that they may outnumber rocky planets in the habitable zone of stars by a few orders of magnitude.

https://arxiv.org/abs/1711.09908
Post by: Star One on 12/01/2017 07:53 PM
Giant black hole pair photobombs Andromeda galaxy

Quote
It seems like even black holes can’t resist the temptation to insert themselves unannounced into photographs. A cosmic photobomb found as a background object in images of the nearby Andromeda galaxy has revealed what could be the most tightly coupled pair of supermassive black holes ever seen.

https://astronomynow.com/2017/12/01/giant-black-hole-pair-photobombs-andromeda-galaxy/

A Microlensing Event Seen from Three Positions in Space

Quote
In a new paper, Yee and a large team of her colleagues report the first microlensing event seen from three well-separated points: Spitzer, the Earth, and the Kepler “K2” mission, which has an orbit similar to that of Spitzer but which currently trails the Earth about one-sixth of the way around in its orbital path. The lensing object, known as MOA-2016-BLG-290, was determined from these measurements to be an extremely low mass star of about .07 solar-masses (seventy-seven Jupiter-masses), and situated about twenty-two thousand light-years away in our galaxy. The result, besides detecting an object intermediate in mass between a star and a planet, demonstrates the power of microlensing parallax measurements predicted decades ago.

https://www.cfa.harvard.edu/news/su201745

The habitability of the Milky Way during the active phase of its central supermassive black hole

Quote
During the peak of their accretion phase, supermassive black holes in galactic cores are known to emit very high levels of ionizing radiation, becoming visible over intergalactic distances as quasars or active galactic nuclei (AGN). Here, we quantify the extent to which the activity of the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*), may have affected the habitability of Earth-like planets in our Galaxy. We focus on the amount of atmospheric loss and on the possible biological damage suffered by planets exposed to X-ray and extreme ultraviolet (XUV) radiation produced during the peak of the active phase of Sgr A*. We find that terrestrial planets could lose a total atmospheric mass comparable to that of present day Earth even at large distances (~1 kiloparsec) from the galactic center. Furthermore, we find that the direct biological damage caused by Sgr A* to surface life on planets not properly screened by an atmosphere was probably significant during the AGN phase, possibly hindering the development of complex life within a few kiloparsecs from the galactic center.

https://arxiv.org/abs/1711.11318
Post by: Star One on 12/05/2017 08:22 PM
Trickle-down is the Solution (to the Planetary Core Formation Problem)

Quote
Scientists have long pondered how rocky bodies in the solar system—including our own Earth—got their metal cores. According to research conducted by The University of Texas at Austin, evidence points to the downwards percolation of molten metal toward the center of the planet through tiny channels between grains of rock.

The finding calls into question the interpretation of prior experiments and simulations that sought to understand how metals behave under intense heat and pressure when planets are forming. Past results suggested that large portions of molten metals stayed trapped in isolated pores between the grains. In contrast, the new research suggests that once those isolated pores grow large enough to connect,  the molten metal starts to flow, and most of it is able to percolate along grain boundaries. This process would let metal trickle down through the mantle, accumulate in the center, and form a metal core, like the iron core at the heart of our home planet.

https://www.jsg.utexas.edu/news/2017/12/trickle-down-is-the-solution-to-the-planetary-core-formation-problem/
Post by: Star One on 12/06/2017 05:54 PM
Researchers find exciting potential for little-known exoplanet – and discover another planet in the process

Quote
New research using data collected by the European Southern Observatory (ESO) has revealed that a little-known exoplanet called K2-18b could well be a scaled-up version of Earth.

Just as exciting, the same researchers also discovered for the first time that the planet has a neighbor.

“Being able to measure the mass and density of K2-18b was tremendous, but to discover a new exoplanet was lucky and equally exciting,” says lead author Ryan Cloutier, a PhD student in U of T Scarborough’s Centre for Planet Science, U of T’s Department of Astronomy and Astrophysics, and Université de Montréal Institute for research on exoplanets (iREx).

Both planets orbit K2-18, a red-dwarf star located about 111 light years away in the constellation Leo. When the planet K2-18b was first discovered in 2015, it was found to be orbiting within the star’s habitable zone, making it an ideal candidate to have liquid surface water, a key element in harbouring conditions for life as we know it.

https://utsc.utoronto.ca/news-events/breaking-research/researchers-find-exciting-potential-little-known-exoplanet-and-discover-another
Post by: Star One on 12/06/2017 08:03 PM
Found: The most distant supermassive black hole ever observed

Quote
A team of astronomers led by Carnegie’s Eduardo Bañados used Carnegie’s Magellan telescopes to discover the most-distant supermassive black hole ever observed. It resides in a luminous quasar and its light reaches us from when the Universe was only 5 percent of its current age — just 690 million years after the Big Bang.

Quasars are tremendously bright objects comprised of enormous black holes accreting matter at the centers of massive galaxies. This newly discovered black hole has a mass that is 800 million times the mass of our Sun.

“Gathering all this mass in fewer than 690 million years is an enormous challenge for theories of supermassive black hole growth,” Bañados explained.

https://astronomynow.com/2017/12/06/found-the-most-distant-supermassive-black-hole-ever-observed/
Post by: jebbo on 12/07/2017 05:20 PM
The E-ELT mirror is now fully funded.

--- Tony
Post by: Star One on 12/12/2017 07:53 PM
Meteorite’s origins point to possible undiscovered asteroid

Quote
A new analysis of a meteorite called Bunburra Rockhole has revealed that the rock originated from a previously unknown parent asteroid, allowing scientists to understand the geology of the parent body.

The parent body was differentiated, meaning that it was large enough to separate into a core, mantle and crust, and was roughly spherical in shape, though not as large as a planet. Identifying a new differentiated asteroid is vital for understanding the formation of asteroids and planets in the Solar System. Most of the large asteroids in the Asteroid Belt are already known, so this means that either the meteorite originated on an asteroid that has been eroded, or there is another large asteroid out there.

Bunburra Rockhole was the first meteorite to be recovered using the Desert Fireball Network, a network of cameras across Australia that observe where meteoroids enter the atmosphere. These cameras make it possible to determine the orbit of a meteorite prior to its descent to Earth. Models of the orbit of Bunburra Rockhole placed its origin within the innermost, main asteroid belt, interior to Vesta, the second-largest body in the Asteroid Belt between Mars and Jupiter.

https://astronomynow.com/2017/12/11/meteorites-origins-point-to-possible-undiscovered-asteroid/
Post by: redliox on 12/12/2017 10:03 PM
Posted an astronomy relevant question in regards to finding out nearest exoplanets:
https://space.stackexchange.com/questions/24010/could-a-21-meter-space-telescope-detect-the-nearest-exoplanets (https://space.stackexchange.com/questions/24010/could-a-21-meter-space-telescope-detect-the-nearest-exoplanets)
Post by: Star One on 12/13/2017 08:01 PM
Amongst the 86 official star names allocated by the IAU Barnard’s Star officially gains that name 100 years after its discovery by Edward Emerson Barnard.

https://www.iau.org/news/pressreleases/detail/iau1707/
Post by: Dao Angkan on 12/13/2017 08:40 PM
Extragalactic exoplanets could be detected by the Large Synoptic Survey Telescope.

Can gravitational microlensing detect extragalactic exoplanets? Self-lensing models of the Small Magellanic Cloud (https://arxiv.org/abs/1712.03986)

Also, ESPRESSO sees first light (https://www.eso.org/public/news/eso1739/). It should achieve precision of at least an order of magnitude over HARPS.
Post by: redliox on 12/13/2017 10:22 PM
Extragalactic exoplanets could be detected by the Large Synoptic Survey Telescope.

Can gravitational microlensing detect extragalactic exoplanets? Self-lensing models of the Small Magellanic Cloud (https://arxiv.org/abs/1712.03986)

Also, ESPRESSO sees first light (https://www.eso.org/public/news/eso1739/). It should achieve precision of at least an order of magnitude over HARPS.

Every time I hear about the discovery of some planet 1,000 light years away...I can't help thinking "And we still don't know how many planets are around Alpha Centauri yet."  At least Proxima b makes a start...

I will say finding exoplanets in an entirely different galaxy is impressive.
Post by: Dao Angkan on 12/14/2017 04:16 PM
Detection by radial velocity is probably the best bet for discovering more planets around the Alpha Centauri system and other relatively nearby stars. ESPRESSO and EXPRES (https://arxiv.org/abs/1606.04413) should help with this in the near term.

Microlensing is great for distant stars, currently several exoplanets have been discovered at over 20,000 LY distance. The Small Magellanic Cloud is ~200,000 LY away.
Post by: the_other_Doug on 12/14/2017 10:45 PM
Has anyone come up with what our own sun's radial velocity perturbations would look like from a variety of distances and with a variety of viewing "resolutions"?

In other words, how easy would it be from 30 light-years away, for example, to examine Sol and state that it has four inner rocky planets and four outer gas / ice giants?  How easy from 300?  From 3,000?  Et cetera...
Post by: Alpha_Centauri on 12/15/2017 12:05 PM
Typical angular resolution isn't the problem with RV as you only need an unresolved blob of light. The main limiting factors are things like getting enough photons to flesh out the spectrum (either use a big enough light bucket / telescope / array, or viewing brighter stars), a high enough spectrograph resolution to separate out absorption lines, and the intrinsic "noise" largely due to stellar activity.

Our Sun has a decent luminosity so would be viewable for spectrographs like ours for quite some distance. It is also pretty quiet in comparison to many stars, so I think it would be on any alien astronomers target list. I don't know about exact figures. Of course on the other hand our solar system has one rather big downside; compared with many other systems most of our planets are quite some distance from our star and so have long orbital periods, so monitoring to get large enough orbital arcs to improve S/N would take some time.

I believe radial velocity observations of sunlight were conducted in the past, especially back when people were first thinking about finding planets using RV in the 90s. There will be papers on it somewhere. Obviously our instruments have inmproved significantly since then.
Post by: jebbo on 12/18/2017 11:24 AM
Two interesting exoplanet papers today

First, more detail of the "Fulton gap" in planet radii:

Exoplanet Radius Gap Dependence on Host Star Type
Quote
Exoplanets smaller than Neptune are numerous, but the nature of the planet populations in the 1-4 Earth radii range remains a mystery. The complete Kepler sample of Q1-Q17 exoplanet candidates shows a radius gap at ~ 2 Earth radii, as reported by us in January 2017 in LPSC conference abstract #1576 (Zeng et al. 2017). A careful analysis of Kepler host stars spectroscopy by the CKS survey allowed Fulton et al. (2017) in March 2017 to unambiguously show this radius gap. The cause of this gap is still under discussion (Ginzburg et al. 2017; Lehmer & Catling 2017; Owen & Wu 2017). Here we add to our original analysis the dependence of the radius gap on host star type.
https://arxiv.org/abs/1712.05458 (https://arxiv.org/abs/1712.05458)

Second, a study of tidal heating in the TRAPPIST-1 system:

Interior Structures and Tidal Heating in the TRAPPIST-1 Planets
Quote
With seven planets, the TRAPPIST-1 system has the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Assuming the planets are composed of non-compressible iron, rock, and H2O, we determine possible interior structures for each planet. To determine how much tidal heat may be dissipated within each planet, we construct a tidal heat generation model using a single uniform viscosity and rigidity for each planet based on the planet's composition. With the exception of TRAPPIST-1c, all seven of the planets have densities low enough to indicate the presence of significant H2O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface, which may be detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳ 0.3. Determining the planet's masses within ∼0.1 to 0.5 Earth masses would confirm or rule out the presence of H2O and/or iron in each planet, and permit detailed models of heat production and transport in each planet. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.
https://arxiv.org/abs/1712.05641 (https://arxiv.org/abs/1712.05641)

I'm still dubious of the density measurements in this system ... they'll be much more certain once we get RV data from instruments like SPIROU

--- Tony

Post by: Star One on 12/18/2017 07:55 PM
Two interesting exoplanet papers today

First, more detail of the "Fulton gap" in planet radii:

Exoplanet Radius Gap Dependence on Host Star Type
Quote
Exoplanets smaller than Neptune are numerous, but the nature of the planet populations in the 1-4 Earth radii range remains a mystery. The complete Kepler sample of Q1-Q17 exoplanet candidates shows a radius gap at ~ 2 Earth radii, as reported by us in January 2017 in LPSC conference abstract #1576 (Zeng et al. 2017). A careful analysis of Kepler host stars spectroscopy by the CKS survey allowed Fulton et al. (2017) in March 2017 to unambiguously show this radius gap. The cause of this gap is still under discussion (Ginzburg et al. 2017; Lehmer & Catling 2017; Owen & Wu 2017). Here we add to our original analysis the dependence of the radius gap on host star type.
https://arxiv.org/abs/1712.05458 (https://arxiv.org/abs/1712.05458)

Second, a study of tidal heating in the TRAPPIST-1 system:

Interior Structures and Tidal Heating in the TRAPPIST-1 Planets
Quote
With seven planets, the TRAPPIST-1 system has the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Assuming the planets are composed of non-compressible iron, rock, and H2O, we determine possible interior structures for each planet. To determine how much tidal heat may be dissipated within each planet, we construct a tidal heat generation model using a single uniform viscosity and rigidity for each planet based on the planet's composition. With the exception of TRAPPIST-1c, all seven of the planets have densities low enough to indicate the presence of significant H2O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface, which may be detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳ 0.3. Determining the planet's masses within ∼0.1 to 0.5 Earth masses would confirm or rule out the presence of H2O and/or iron in each planet, and permit detailed models of heat production and transport in each planet. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.
https://arxiv.org/abs/1712.05641 (https://arxiv.org/abs/1712.05641)

I'm still dubious of the density measurements in this system ... they'll be much more certain once we get RV data from instruments like SPIROU

--- Tony

First paper listed above comes under criticism for being an example of ‘flag planting’, half finished and not the appropriate forum for discussing the topic.

Post by: jebbo on 12/19/2017 06:27 AM
First paper listed above comes under criticism for being an example of ‘flag planting’, half finished and not the appropriate forum for discussing the topic.

Yes, I saw that ... it was a discussion over the purpose of the (extremely new) "Research Notes" rather than a critique of the paper (don't think anyone questioned the data).  To me, leaving aside the flag-planting issue, it seems in the spirit of RN: small contributions that either need follow-up or are not worth a paper in their own right.

The wider discussion surrounding this bit was more interesting: when should effects be named after people.

--- Tony
Post by: Star One on 12/19/2017 06:37 AM
First paper listed above comes under criticism for being an example of ‘flag planting’, half finished and not the appropriate forum for discussing the topic.

Yes, I saw that ... it was a discussion over the purpose of the (extremely new) "Research Notes" rather than a critique of the paper (don't think anyone questioned the data).  To me, leaving aside the flag-planting issue, it seems in the spirit of RN: small contributions that either need follow-up or are not worth a paper in their own right.

The wider discussion surrounding this bit was more interesting: when should effects be named after people.

--- Tony

Yes I noticed the naming issue. I know Twitter isn’t a very good basis for judging these things but the consensus seemed to be against the naming in this case
Post by: jebbo on 12/19/2017 07:00 AM
Yes I noticed the naming issue. I know Twitter isn’t a very good basis for judging these things but the consensus seemed to be against the naming in this case

Yes ... hardly surprising as the whole "Fulton gap" name was really just a bit of a running gag on Twitter.  Photo-evaporation valley is short and descriptive enough.

--- Tony
Post by: as58 on 12/19/2017 07:59 AM
I must admit that I don't see the point of RNAAS when everything is put on arxiv anyway. To me it seems like a flag-planting operation by AAS...
Post by: jebbo on 12/20/2017 08:41 AM
Predictions of planet detections with near infrared radial velocities in the up-coming SPIRou Legacy Survey-Planet Search
Quote
The SPIRou near infrared spectro-polarimeter is destined to begin science operations at the Canada-France-Hawaii Telescope in mid-2018. One of the instrument's primary science goals is to discover the closest exoplanets to the Solar System by conducting a 3-5 year long radial velocity survey of nearby M dwarfs at an expected precision of ∼1 m s−1; the SPIRou Legacy Survey-Planet Search (SLS-PS). In this study we conduct a detailed Monte-Carlo simulation of the SLS-PS using our current understanding of the occurrence rate of M dwarf planetary systems and physical models of stellar activity. From simultaneous modelling of planetary signals and activity, we predict the population of planets detected in the SLS-PS. With our fiducial survey strategy and expected instrument performance over a nominal survey length of ∼3 years, we expect SPIRou to detect 85.3+29.3−12.4 planets including 20.0+16.8−7.2 habitable zone planets and 8.1+7.6−3.2 Earth-like planets from a sample of 100 M1-M8.5 dwarfs out to 11 pc. By studying mid-to-late M dwarfs previously inaccessible to existing optical velocimeters, SPIRou will put meaningful constraints on the occurrence rate of planets around those stars including the value of η⊕ at an expected level of precision of ≲45%. We also predict a subset of 46.7+16.0−6.0 planets may be accessible with dedicated high-contrast imagers on the next generation of ELTs including 4.9+4.7−2.0 potentially imagable Earth-like planets. Lastly, we compare the results of our fiducial survey strategy to other foreseeable survey versions to quantify which strategy is optimized to reach the SLS-PS science goals. The results of our simulations are made available to the community on github.
https://arxiv.org/abs/1712.06673 (https://arxiv.org/abs/1712.06673)

I'm looking forward to the results from this one!  First, it should give us much better masses for Proxima b and the TRAPPIST-1 planets; second, it should yield a few direct imaging targets for the forthcoming 30m class telescopes.

--- Tony
Post by: Star One on 12/20/2017 08:07 PM
Giant Bubbles on Red Giant Star’s Surface

Quote
Astronomers using ESO’s Very Large Telescope have for the first time directly observed granulation patterns on the surface of a star outside the Solar System — the ageing red giant π1 Gruis. This remarkable new image from the PIONIER instrument reveals the convective cells that make up the surface of this huge star, which has 350 times the diameter of the Sun. Each cell covers more than a quarter of the star’s diameter and measures about 120 million kilometres across. These new results are being published this week in the journal Nature.

http://www.eso.org/public/news/eso1741/

Post by: Star One on 12/22/2017 07:24 PM
The cool and distant formation of Mars

Quote
With approximately one ninth of Earth's mass, Mars is widely considered to be a stranded planetary embryo that never became a fully-grown planet. A currently popular planet formation theory predicts that Mars formed near Earth and Venus and was subsequently scattered outwards to its present location. In such a scenario, the compositions of the three planets are expected to be similar to each other. However, bulk elemental and isotopic data for martian meteorites demonstrate that key aspects of Mars' composition are markedly different from that of Earth. This suggests that Mars formed outside of the terrestrial feeding zone during primary accretion. It is therefore probable that Mars always remained significantly farther from the Sun than Earth; its growth was stunted early and its mass remained relatively low. Here we identify a potential dynamical pathway that forms Mars in the asteroid belt and keeps it outside of Earth's accretion zone while at the same time accounting for strict age and compositional constraints, as well as mass differences. Our uncommon pathway (approximately 2% probability) is based on the Grand Tack scenario of terrestrial planet formation, in which the radial migration by Jupiter gravitationally sculpts the planetesimal disc at Mars' current location. We conclude that Mars' formation requires a specific dynamical pathway, while this is less valid for Earth and Venus. We further predict that Mars' volatile budget is most likely different from Earth's and that Venus formed close enough to our planet that it is expected to have a nearly identical composition from common building blocks.

http://www.sciencedirect.com/science/article/pii/S0012821X1730184X?via%3Dihub#!

https://arxiv.org/pdf/1704.00184.pdf
Post by: Star One on 12/28/2017 05:05 PM
The origins of our solar system?

Triggered Star Formation inside the Shell of a Wolf–Rayet Bubble as the Origin of the Solar System

Quote
A critical constraint on solar system formation is the high ${}^{26}\mathrm{Al}$/27Al abundance ratio of $5\times {10}^{-5}$ at the time of formation, which was about 17 times higher than the average Galactic ratio, while the 60Fe/56Fe value was about $2\times {10}^{-8}$, lower than the Galactic value. This challenges the assumption that a nearby supernova (SN) was responsible for the injection of these short-lived radionuclides into the early solar system. We show that this conundrum can be resolved if the solar system was formed by a triggered star formation at the edge of a Wolf–Rayet (W–R) bubble. 26Al is produced during the evolution of the massive star, released in the wind during the W–R phase, and condenses into dust grains that are seen around W–R stars. The dust grains survive passage through the reverse shock and the low-density shocked wind, reach the dense shell swept-up by the bubble, detach from the decelerated wind, and are injected into the shell. Some portions of this shell subsequently collapse to form the dense cores that give rise to solar-type systems. The subsequent aspherical SN does not inject appreciable amounts of ${}^{60}\mathrm{Fe}$ into the proto–solar system, thus accounting for the observed low abundance of ${}^{60}\mathrm{Fe}$. We discuss the details of various processes within the model and conclude that it is a viable model that can explain the initial abundances of ${}^{26}\mathrm{Al}$ and ${}^{60}\mathrm{Fe}$. We estimate that 1%–16% of all Sun-like stars could have formed in such a setting of triggered star formation in the shell of a W–R bubble.

http://iopscience.iop.org/article/10.3847/1538-4357/aa992e/meta
Post by: ExoExplorer on 01/03/2018 05:29 PM
Predictions of planet detections with near infrared radial velocities in the up-coming SPIRou Legacy Survey-Planet Search
Quote
The SPIRou near infrared spectro-polarimeter is destined to begin science operations at the Canada-France-Hawaii Telescope in mid-2018. One of the instrument's primary science goals is to discover the closest exoplanets to the Solar System by conducting a 3-5 year long radial velocity survey of nearby M dwarfs at an expected precision of ∼1 m s−1; the SPIRou Legacy Survey-Planet Search (SLS-PS). In this study we conduct a detailed Monte-Carlo simulation of the SLS-PS using our current understanding of the occurrence rate of M dwarf planetary systems and physical models of stellar activity. From simultaneous modelling of planetary signals and activity, we predict the population of planets detected in the SLS-PS. With our fiducial survey strategy and expected instrument performance over a nominal survey length of ∼3 years, we expect SPIRou to detect 85.3+29.3−12.4 planets including 20.0+16.8−7.2 habitable zone planets and 8.1+7.6−3.2 Earth-like planets from a sample of 100 M1-M8.5 dwarfs out to 11 pc. By studying mid-to-late M dwarfs previously inaccessible to existing optical velocimeters, SPIRou will put meaningful constraints on the occurrence rate of planets around those stars including the value of η⊕ at an expected level of precision of ≲45%. We also predict a subset of 46.7+16.0−6.0 planets may be accessible with dedicated high-contrast imagers on the next generation of ELTs including 4.9+4.7−2.0 potentially imagable Earth-like planets. Lastly, we compare the results of our fiducial survey strategy to other foreseeable survey versions to quantify which strategy is optimized to reach the SLS-PS science goals. The results of our simulations are made available to the community on github.
https://arxiv.org/abs/1712.06673 (https://arxiv.org/abs/1712.06673)

I'm looking forward to the results from this one!  First, it should give us much better masses for Proxima b and the TRAPPIST-1 planets; second, it should yield a few direct imaging targets for the forthcoming 30m class telescopes.

--- Tony
SLS-PS is unlikely to detect the radial velocity of TRAPPIST-1 (mv = 19). It's just simply too faint for Doppler spectroscopy.
Post by: jebbo on 01/03/2018 05:39 PM
SLS-PS is unlikely to detect the radial velocity of TRAPPIST-1 (mv = 19). It's just simply too faint for Doppler spectroscopy.

Yes, it is very dim in the V band, but it is much brighter in IR. Also, I didn't post that blind, I asked them ages ago:

Quote
with IR mags of J=11, H=10.7 and K=10.3, Trappist-1 is in reach of SPIRou_astro. no doubt SPIRou_astro will look at it once on CFHT

Quote
W/ expected RV amplitudes of 0.9 to 3.5m/s, Trappist-1 planets b to h may be better characterized in mass & density w/ SPIRou_astro

--- Tony

Post by: ExoExplorer on 01/03/2018 05:53 PM
Typical angular resolution isn't the problem with RV as you only need an unresolved blob of light. The main limiting factors are things like getting enough photons to flesh out the spectrum (either use a big enough light bucket / telescope / array, or viewing brighter stars), a high enough spectrograph resolution to separate out absorption lines, and the intrinsic "noise" largely due to stellar activity.

Our Sun has a decent luminosity so would be viewable for spectrographs like ours for quite some distance. It is also pretty quiet in comparison to many stars, so I think it would be on any alien astronomers target list. I don't know about exact figures. Of course on the other hand our solar system has one rather big downside; compared with many other systems most of our planets are quite some distance from our star and so have long orbital periods, so monitoring to get large enough orbital arcs to improve S/N would take some time.

I believe radial velocity observations of sunlight were conducted in the past, especially back when people were first thinking about finding planets using RV in the 90s. There will be papers on it somewhere. Obviously our instruments have inmproved significantly since then.
The orbital inclination of the alien Earth would also limit the measurable amplitude of wobble. For example, if the inclination is close to 0°, the planet would be undetectable by RV regardless of how precise.
Post by: ExoExplorer on 01/03/2018 06:23 PM
SLS-PS is unlikely to detect the radial velocity of TRAPPIST-1 (mv = 19). It's just simply too faint for Doppler spectroscopy.

Yes, it is very dim in the V band, but it is much brighter in IR. Also, I didn't post that blind, I asked them ages ago:

Quote
with IR mags of J=11, H=10.7 and K=10.3, Trappist-1 is in reach of SPIRou_astro. no doubt SPIRou_astro will look at it once on CFHT

Quote
W/ expected RV amplitudes of 0.9 to 3.5m/s, Trappist-1 planets b to h may be better characterized in mass & density w/ SPIRou_astro

--- Tony
How surprising. I thought it would be impossible in the short-term, but the outer three planets are hardly achievable since low-density materials like ice probably make up a significant part of their masses. Combination of RV and TTV would constrain the whole system with better precision I believe.
Post by: Star One on 01/09/2018 05:00 PM
Extra-Terrestrial Hypatia Stone Rattles Solar System Status Quo

https://scienmag.com/extra-terrestrial-hypatia-stone-rattles-solar-system-status-quo/
Post by: Bynaus on 01/09/2018 06:58 PM
Extra-Terrestrial Hypatia Stone Rattles Solar System Status Quo

https://scienmag.com/extra-terrestrial-hypatia-stone-rattles-solar-system-status-quo/

A couple of years ago, I was co-author on a paper studying the Hypatia stone (https://arxiv.org/abs/1510.06594). The stone is clearly extraterrestrial, yes, but I think this whole story is getting blown way out of proportion in the new paper.

First, its not like carbon-dominated materials are unheard off in meteorites - we identified several possibilities in our paper, the strongest, in my opinion, being that the stone is shock-compressed (thus diamond-bearing) graphite nodule from an iron meteorite (there is actually additional support for this from the Fe, Ni, S and P phases the authors of the new paper report - all these elements are abundant in iron meteorites).

Second, the claim of a pre-solar origin would require the identification of the characteristically large isotopic anomalies, which the authors of the new paper do not report.
Post by: Star One on 01/09/2018 08:13 PM
White dwarf’s inner makeup is mapped for the first time

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Astronomers have probed the inner life of a dead star. Tiny changes in a white dwarf’s brightness reveal that the stellar corpse has more oxygen in its core than expected, researchers report online January 8 in Nature. The finding could challenge theories of how stars live and die, and may have implications for measuring the expansion of the universe.

Quote
More recent observations suggest that these so-called standard candles may not be so standard after all. If the white dwarfs that help create supernovas have varying oxygen contents, that may help explain some of the differences, Fontaine says.

Accounting for that difference may someday help reveal details of what dark energy is made of, says astrophysicist Alexei Filippenko of the University of California, Berkeley. But those implications are a long way off. “Just how much bearing it will have on cosmology remains to be seen,” he says.

https://www.sciencenews.org/article/white-dwarfs-inner-makeup-mapped-first-time
Post by: fthomassy on 01/09/2018 10:38 PM
Cross posting as it might relate to astronomy tracking too ...
Incredible footage of stage sep and the boostback burn.

Thanks!  That was my video. I'm hoping at some point other launch regulars who do tracking shots start to adopt my setup and software for their shots as well.  The software is very experimental, but it's freely available.  Computer, joystick, and telescope not included, of course.
Post by: Star One on 01/10/2018 07:17 PM
Across the universe, fast radio bursts ‘shout and twist’

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An international group of astronomers has found that the Cornell-discovered fast radio burst FRB 121102 – a brief, gigantic pulse of radio waves from 3 billion light years away – passes through a veil of magnetized plasma. This causes the cosmic blasts to “shout and twist,” which will help the scientists determine the source.

The research is featured on the cover of Nature, Jan. 11.

The “shouting” represents the bursts, and the “twisting” describes a physical phenomenon called Faraday rotation, which occurs as radio waves pass through a magnetized plasma, explained James Cordes, the George Feldstein Professor of Astronomy. Measurement of the twisting provides further scientific detail on the origin of FRB 121102. The data were culled from the Arecibo Observatory in Puerto Rico and confirmed by Green Bank Observatory in West Virginia.

Post by: Star One on 01/11/2018 08:52 PM
The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

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K2-138 is a moderately bright (V = 12.2, K = 10.3) main-sequence K star observed in Campaign 12 of the NASA K2 mission. It hosts five small (1.6–3.3 ${R}_{\oplus }$) transiting planets in a compact architecture. The periods of the five planets are 2.35, 3.56, 5.40, 8.26, and 12.76 days, forming an unbroken chain of near 3:2 resonances. Although we do not detect the predicted 2–5 minute transit timing variations (TTVs) with the K2 timing precision, they may be observable by higher-cadence observations with, for example, Spitzer or CHEOPS. The planets are amenable to mass measurement by precision radial velocity measurements, and therefore K2-138 could represent a new benchmark system for comparing radial velocity and TTV masses. K2-138 is the first exoplanet discovery by citizen scientists participating in the Exoplanet Explorers project on the Zooniverse platform.

http://iopscience.iop.org/article/10.3847/1538-3881/aa9be0
Post by: jebbo on 01/12/2018 09:31 AM
The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

Yes, this is a very interesting one: the two transits at ~42 days that suggest a sixth planet are consistent with the 3/2 resonance chain ... if you skip two slots at ~18.6 days and 27.9 days

--- Tony
Post by: Star One on 01/12/2018 09:35 AM
The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

Yes, this is a very interesting one: the two transits at ~42 days that suggest a sixth planet are consistent with the 3/2 resonance chain ... if you skip two slots at ~18.6 days and 27.9 days

--- Tony

Go and have a quick look at Professor Chris Lintott’s twitter account as he talks about that very thing on there.
Post by: Star One on 01/12/2018 12:53 PM
Meet the amateur astronomers who track secretive spy satellites for fun

https://www.popsci.com/zuma-spy-satellite-amateur-astronomer
Post by: Star One on 01/12/2018 07:36 PM
We may be able to see mountains and valleys on distant worlds

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Moiya McTier at Columbia University in New York presented her research into the embryonic field of exotopography on 11 January at a meeting of the American Astronomical Society. She says that by analysing the dip in a star’s light as a planet passes in front of it, we might be able to discern actual details about the planet’s landscape.

None of the rocky planets in our solar system are perfectly round: there are mountains, canyons, craters and other features that carve elevations high and low across a surface. So why shouldn’t there be similar features on planets orbiting other stars?

McTier took US Geological Survey maps of our four terrestrial planets and the Moon to determine what their light curve around

https://www.newscientist.com/article/2158466-we-may-be-able-to-see-mountains-and-valleys-on-distant-worlds
Post by: CuddlyRocket on 01/13/2018 05:53 PM
The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

Yes, this is a very interesting one: the two transits at ~42 days that suggest a sixth planet are consistent with the 3/2 resonance chain ... if you skip two slots at ~18.6 days and 27.9 days

55.8 days, and any multiple thereof, is a whole number multiple of both 18.6 and 27.9. So, perhaps there's something larger with such an orbital period, but not a multiple of ~42 days, that disrupted the formation of any planets at those two slots? If the orbital period is long enough it might not have transited during the observation run.
Post by: Star One on 01/16/2018 07:33 PM
Ingredients for life revealed in meteorites that fell to Earth

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Two wayward space rocks, which separately crashed to Earth in 1998 after circulating in our solar system’s asteroid belt for billions of years, share something else in common: the ingredients for life. They are the first meteorites found to contain both liquid water and a mix of complex organic compounds such as hydrocarbons and amino acids.

A detailed study of the chemical makeup within tiny blue and purple salt crystals sampled from these meteorites, which included results from X-ray experiments at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), also found evidence for the pair’s past intermingling and likely parents. These include Ceres, a brown dwarf planet that is the largest object in the asteroid belt, and the asteroid Hebe, a major source of meteorites that fall on Earth.

https://astronomynow.com/2018/01/16/ingredients-for-life-revealed-in-meteorites-that-fell-to-earth/
Post by: jgoldader on 01/16/2018 08:36 PM
Ingredients for life revealed in meteorites that fell to Earth

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Two wayward space rocks, which separately crashed to Earth in 1998 after circulating in our solar system’s asteroid belt for billions of years, share something else in common: the ingredients for life. They are the first meteorites found to contain both liquid water and a mix of complex organic compounds such as hydrocarbons and amino acids.

A detailed study of the chemical makeup within tiny blue and purple salt crystals sampled from these meteorites, which included results from X-ray experiments at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), also found evidence for the pair’s past intermingling and likely parents. These include Ceres, a brown dwarf planet that is the largest object in the asteroid belt, and the asteroid Hebe, a major source of meteorites that fall on Earth.

https://astronomynow.com/2018/01/16/ingredients-for-life-revealed-in-meteorites-that-fell-to-earth/

I'm pretty sure I remember a while back reading about water from the ancient Earth discovered in salt crystals from fossilized rocks... ah, here it is!

https://www.sciencedaily.com/releases/2001/12/011210163624.htm

This new study looks to be in a similar spirit.  (Boy, it really WAS a while back!)  Awfully interesting stuff.
Post by: Star One on 01/17/2018 08:11 PM
The Third Workshop on Extremely Precise Radial Velocities: The New Instruments

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The Third Workshop on Extremely Precise Radial Velocities was held at the Penn Stater Conference Center and Hotel in State College, Pennsylvania, USA from 2016 August 14 to 17, and featured over 120 registrants from around the world. Here we provide a brief description of the conference, its format, and its session topics and chairs. 23 instrument teams were represented in plenary talks, and we present a table containing the basic characteristics of their new precise Doppler velocimeters.

https://arxiv.org/abs/1801.05383
Post by: Star One on 01/18/2018 07:33 PM
Using Gravitational-wave Observations and Quasi-universal Relations to Constrain the Maximum Mass of Neutron Stars

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Combining the GW observations of merging systems of binary neutron stars and quasi-universal relations, we set constraints on the maximum mass that can be attained by nonrotating stellar models of neutron stars. More specifically, exploiting the recent observation of the GW event GW170817 and drawing from basic arguments on kilonova modeling of GRB 170817A together with the quasi-universal relation between the maximum mass of nonrotating stellar models ${M}_{\mathrm{TOV}}$ and the maximum mass supported through uniform rotation ${M}_{\max }\,=({1.20}_{-0.05}^{+0.02}){M}_{\mathrm{TOV}}$, we set limits for the maximum mass to be ${2.01}_{-0.04}^{+0.04}\leqslant {M}_{\mathrm{TOV}}/{M}_{\odot }\lesssim {2.16}_{-0.15}^{+0.17}$, where the lower limit in this range comes from pulsar observations. Our estimate, which follows a very simple line of arguments and does not rely on the modeling of the electromagnetic signal in terms of numerical simulations, can be further refined as new detections become available. We briefly discuss the impact that our conclusions have on the equation of state of nuclear matter.

http://iopscience.iop.org/article/10.3847/2041-8213/aaa401/meta

New Titan Findings from Topographical Map

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Cassini’s huge dataset will yield discoveries for many years, as witness the global topographical map of Titan that has been assembled by Cornell University astronomers. The map draws on topographical data of the moon from multiple sources by way of studying its terrain and the flow of its surface liquids. Bear in mind that only 9 percent of Titan has been observed at relatively high resolution, and another 25-30 percent at lower resolution. For the remainder, the team mapped the surface using an interpolation algorithm and a global minimization process described in the first of two papers in Geophysical Review Letters.

https://www.centauri-dreams.org/?p=39157
Post by: jebbo on 01/19/2018 07:57 AM
Interesting proposal for a large space-based telescope to hunt for biosignatures ... this is the first ESA L4 idea I've seen (might be premature to create an ESA L4 mission competition thread ;) )

Personally, in that time frame, I'd be thinking about on-orbit assembly rather than single fairing-limited launch.

SUPERSHARP - Segmented Unfolding Primary for Exoplanet Research via Spectroscopic High Angular Resolution Photography

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We propose to search for biosignatures in the spectra of reflected light from about 100 Earth-sized planets that are already known to be orbiting in their habitable zones (HZ). For a sample of G and K type hosts, most of these planets will be between 25 and 50 milli-arcsec (mas) from their host star and 1 billion to 10 billion times fainter. To separate the planet's image from that of its host star at the wavelength (763nm) of the oxygen biosignature we need a telescope with an aperture of 16 metres. Furthermore, the intensity of the light from the host star at the position in the image of the exoplanet must be suppressed otherwise the exoplanet will be lost in the glare.
This presents huge technical challenges. The Earth's atmosphere is turbulent which makes it impossible to achieve the required contrast from the ground at 763nm. The telescope therefore needs to be in space and to fit the telescope in the rocket fairing it must be a factor of 4 or more times smaller when folded than when operational. To obtain spectroscopy of the planet's biosignature at 763nm we need to use an integral field spectrometer (IFS) with a field of view (FOV) of 1000 x 1000 milli-arcsec (mas) and a spectral resolution of 100. This is a device that simultaneously takes many pictures of the exoplanet each at a slightly different wavelength which are then recorded as a data cube with two spatial dimensions and one wavelength dimension. In every data cube wavelength slice, the background light from the host star at the location of the planet image must be minimised. This is achieved via a coronagraph which blocks the light from the host star and active/adaptive optics techniques which continuously maintain very high accuracy optical alignment to make the images as sharp as possible. These are the technical challenges to be addressed in a design study.

https://arxiv.org/abs/1801.06111 (https://arxiv.org/abs/1801.06111)

--- Tony
Post by: Star One on 01/19/2018 08:48 PM
Neutron star merger yields new puzzle for astrophysicists

https://astronomynow.com/2018/01/19/neutron-star-merger-yields-new-puzzle-for-astrophysicists/
Post by: Star One on 01/23/2018 08:06 PM
Evidence of an Upper Bound on the Masses of Planets and Its Implications for Giant Planet Formation

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Celestial bodies with a mass of $M\approx 10\,{M}_{\mathrm{Jup}}$ have been found orbiting nearby stars. It is unknown whether these objects formed like gas-giant planets through core accretion or like stars through gravitational instability. I show that objects with $M\lesssim 4\,{M}_{\mathrm{Jup}}$ orbit metal-rich solar-type dwarf stars, a property associated with core accretion. Objects with $M\gtrsim 10\,{M}_{\mathrm{Jup}}$ do not share this property. This transition is coincident with a minimum in the occurrence rate of such objects, suggesting that the maximum mass of a celestial body formed through core accretion like a planet is less than $10\,{M}_{\mathrm{Jup}}$. Consequently, objects with $M\gtrsim 10\,{M}_{\mathrm{Jup}}$ orbiting solar-type dwarf stars likely formed through gravitational instability and should not be thought of as planets. Theoretical models of giant planet formation in scaled minimum-mass solar nebula Shakura–Sunyaev disks with standard parameters tuned to produce giant planets predict a maximum mass nearly an order of magnitude larger. To prevent newly formed giant planets from growing larger than $10\,{M}_{\mathrm{Jup}}$, protoplanetary disks must therefore be significantly less viscous or of lower mass than typically assumed during the runaway gas accretion stage of giant planet formation. Either effect would act to slow the Type I/II migration of planetary embryos/giant planets and promote their survival. These inferences are insensitive to the host star mass, planet formation location, or characteristic disk dissipation time.

http://iopscience.iop.org/article/10.3847/1538-4357/aa961c

Medium-sized satellites of large Kuiper belt objects

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While satellites of mid- to small-Kuiper belt objects tend to be similar in size and brightness to their primaries, the largest Kuiper belt objects preferentially have satellites with small fractional brightness. In the two cases where the sizes and albedos of the small faint satellites have been measured, these satellites are seen to be small icy fragments consistent with collisional formation. Here we examine Dysnomia and Vanth, the satellites of Eris and Orcus, respectively. Using the Atacama Large Millimeter Array, we obtain the first spatially resolved observations of these systems at thermal wavelengths. We find a diameter for Dysnomia of 700±115 km and for Vanth of 475+/-75 km, with albedos of 0.04_+0.02_-0.01 and 0.08+/-0.02 respectively. Both Dysnomia and Vanth are indistinguishable from typical Kuiper belt objects of their size. Potential implications for the formation of these types of satellites are discussed.

https://arxiv.org/abs/1801.07221