Author Topic: Astronomy Thread  (Read 36221 times)

Offline Star One

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Re: Astronomy Thread
« Reply #260 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

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(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.

Online jebbo

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Re: Astronomy Thread
« Reply #261 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

Offline Star One

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Re: Astronomy Thread
« Reply #262 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?

Online jebbo

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Re: Astronomy Thread
« Reply #263 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

--- Tony
« Last Edit: 11/16/2017 10:02 AM by jebbo »

Offline Star One

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Re: Astronomy Thread
« Reply #264 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

--- Tony

Is Ross 128b just a bit to far then for these instruments?

Online jebbo

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Re: Astronomy Thread
« Reply #265 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

Offline Star One

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Re: Astronomy Thread
« Reply #266 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.

Online jebbo

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Re: Astronomy Thread
« Reply #267 on: 11/16/2017 03:55 PM »
No, it's probably in range for the 30m class of telescopes.

--- Tony

Offline Star One

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Re: Astronomy Thread
« Reply #268 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.

Offline Star One

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Re: Astronomy Thread
« Reply #269 on: 11/20/2017 04:23 PM »
A Case for an Atmosphere on Super-Earth 55 Cancri e

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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

Offline Star One

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Astronomy Thread
« Reply #270 on: 11/20/2017 04:53 PM »
Giant telescope’s mobile-phone ‘dead zones’ rile South African residents

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

https://www.nature.com/news/giant-telescope-s-mobile-phone-dead-zones-rile-south-african-residents-1.22998
« Last Edit: 11/20/2017 04:54 PM by Star One »

Offline Star One

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Astronomy Thread
« Reply #271 on: 11/20/2017 07:18 PM »
Phil Plait debunks the latest moon hoax nonsense and despairs that even Newsweek reproduced these ridiculous claims.

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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
« Last Edit: 11/20/2017 07:19 PM by Star One »

Offline Star One

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Re: Astronomy Thread
« Reply #272 on: 11/28/2017 05:15 PM »
Seeing Double with K2: Testing Re-inflation with Two Remarkably Similar Planets around Red Giant Branch Stars

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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

Offline Star One

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Re: Astronomy Thread
« Reply #273 on: 11/30/2017 08:56 PM »
Subsurface Exolife

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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

Offline Star One

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Astronomy Thread
« Reply #274 on: 12/01/2017 07:53 PM »
Giant black hole pair photobombs Andromeda galaxy

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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

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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

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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
« Last Edit: 12/01/2017 08:08 PM by Star One »

Offline Star One

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Re: Astronomy Thread
« Reply #275 on: 12/05/2017 08:22 PM »
Trickle-down is the Solution (to the Planetary Core Formation Problem)

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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/

Offline Star One

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Astronomy Thread
« Reply #276 on: 12/06/2017 05:54 PM »
Researchers find exciting potential for little-known exoplanet – and discover another planet in the process

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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
« Last Edit: 12/06/2017 05:55 PM by Star One »

Offline Star One

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Re: Astronomy Thread
« Reply #277 on: 12/06/2017 08:03 PM »
Found: The most distant supermassive black hole ever observed

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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.

Their findings are published by Nature.

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/

Online jebbo

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Re: Astronomy Thread
« Reply #278 on: 12/07/2017 05:20 PM »

Offline Star One

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Re: Astronomy Thread
« Reply #279 on: 12/12/2017 07:53 PM »
Meteorite’s origins point to possible undiscovered asteroid

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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/