Author Topic: Astronomy Thread  (Read 61770 times)

Online jebbo

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Re: Exoplanets And Stars Thread
« Reply #240 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/1710.11100

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
« Last Edit: 11/01/2017 09:02 AM by jebbo »

Offline Star One

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Exoplanets And Stars Thread
« Reply #241 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/1710.11100

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

They were talking about this on BBC Radio 4 this morning and interviewing one of the scientists involved in the discovery.

Wouldn’t one answer by that this was a wandering planet that was captured by this star?
« Last Edit: 11/01/2017 12:09 PM by Star One »

Offline CuddlyRocket

Re: Exoplanets And Stars Thread
« Reply #242 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!

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #243 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.

Offline clongton

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Re: Exoplanets And Stars Thread
« Reply #244 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.
« Last Edit: 11/02/2017 03:43 PM by clongton »
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Online jebbo

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Re: Exoplanets And Stars Thread
« Reply #245 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

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #246 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

Offline CuddlyRocket

Re: Exoplanets And Stars Thread
« Reply #247 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.

Offline Star One

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Exoplanets And Stars Thread
« Reply #248 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
« Last Edit: 11/03/2017 11:07 PM by Star One »

Offline Alpha_Centauri

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Re: Exoplanets And Stars Thread
« Reply #249 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.
« Last Edit: 11/03/2017 11:59 PM by Alpha_Centauri »

Offline Bynaus

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Re: Exoplanets And Stars Thread
« Reply #250 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".

Offline CuddlyRocket

Re: Exoplanets And Stars Thread
« Reply #251 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.

Offline Dao Angkan

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Re: Exoplanets And Stars Thread
« Reply #252 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)

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☉.
« Last Edit: 11/06/2017 06:24 PM by Dao Angkan »

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #253 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/

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #254 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

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #255 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.

https://www.eurekalert.org/pub_releases/2017-11/lmsu-mbh110817.php

Offline Star One

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Re: Astronomy Thread
« Reply #256 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

Offline Star One

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Re: Astronomy Thread
« Reply #257 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

Offline CuddlyRocket

Re: Astronomy Thread
« Reply #258 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

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!

Offline Star One

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Re: Astronomy Thread
« Reply #259 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

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.