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Unmanned _ Telescopic Observations _ Exoplanet Discoveries

Posted by: PhilCo126 Apr 21 2009, 11:10 AM

Well-known exoplanet researcher Dr Michel Mayor ( discoverer of Peg 51b with Dr Didier Queloz in 1995 ) today announced the discovery of the lightest exoplanet found so far. The planet, “e”, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist:

Posted by: belleraphon1 Oct 19 2009, 01:32 PM

32 New Exoplanets Found - 10/19/09 ESO release

"Today, at an international ESO/CAUP exoplanet conference in Porto, the team who built the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for ESO's 3.6-metre telescope, reports on the incredible discovery of some 32 new exoplanets, cementing HARPS's position as the world’s foremost exoplanet hunter. This result also increases the number of known low-mass planets by an impressive 30%. Over the past five years HARPS has spotted more than 75 of the roughly 400 or so exoplanets now known"

From searching Extrasolar Planets Encyclopedia catalog I find 6 of the new planets seem to be Neptune mass or less.

BD-082823b at .045 Jmass
GJ 433b at .019 Jmass
GJ 667Cb at .018 Jmass
HD 1255995b at .045 Jmass
HD 215497b at .017Jmass
HD 90156b .055Jmass


Posted by: Julius Oct 20 2009, 11:10 AM

How can they be so sure that the super earths detected represent one planetary body ie.could it not be that 8 earth masses could represent 2 terrestrial planets and other planetary dust the likes of asteroids in orbit round the parent star?!

Posted by: qraal Oct 20 2009, 11:27 AM

QUOTE (Julius @ Oct 20 2009, 10:10 PM) *
How can they be so sure that the super earths detected represent one planetary body ie.could it not be that 8 earth masses could represent 2 terrestrial planets and other planetary dust the likes of asteroids in orbit round the parent star?!

Because the radial velocity detection method detects a periodic signal that only a planet can cause - though some data is too patchy to be sure we're seeing one planet and not two. A diffuse asteroid belt would produce a symmetric 'tug' on the star it orbits, thus producing no radial velocity signal.

Posted by: Greg Hullender Oct 20 2009, 07:47 PM

There's a branch of mathematics called "Fourier Analysis" which, among other things, let's you take a complex signal and break it into a collection of sine waves. It's pretty cool, if you haven't seen it before.

So if there's just one planet, then the velocity plot ought to be a pretty clean simple sine wave over time. If there are multiple planets (let's say three) around the same star, then it'll be a mess, but a fourier analysis ought to result in just three sine curves and very little else.


Posted by: tfisher Oct 22 2009, 12:30 AM

QUOTE (Greg Hullender @ Oct 20 2009, 02:47 PM) *
So if there's just one planet, then the velocity plot ought to be a pretty clean simple sine wave over time. If there are multiple planets (let's say three) around the same star, then it'll be a mess, but a fourier analysis ought to result in just three sine curves and very little else.

I'm afraid this skips over a few important complexities. One is that with eccentric orbits (which are common!), the radial velocity signal of a planet is not a single sine wave, but may have significantly different shape. Another problem is that in reality we never have continuous or even a complete discrete series of radial velocity observations of a given target. Instead of seeing a continuous curve, we just have a non-uniformly spaced discrete sampling from the curve. So Fourier analysis can't really be directly applied to work out the component curves. A third problem is that there is a lot of noise in the observed radial velocities, coming from stellar activity of the host star and limitations of the observation instruments. In many cases (smaller, more distant planets or younger, more active stars) this noise is of a similar or even much greater strength to the signals we are looking for.

You can get a really good understanding of all of this playing with the amazing "systemic console" free tool for fitting candidate planetary systems to radial velocity datasets. You can get this at I highly recommend it!

Posted by: Greg Hullender Oct 22 2009, 02:26 AM

QUOTE (tfisher @ Oct 21 2009, 05:30 PM) *
I'm afraid this skips over a few important complexities.

Fair enough. I still maintain that a Fourier Transform would work fine for a system whose planets had circular orbits and ought to be a great way to eliminate the high-frequency noise in any case, but, yeah, I agree it won't be very good for elliptical orbits.
QUOTE (tfisher @ Oct 21 2009, 05:30 PM) *
You can get a really good understanding of all of this playing with the amazing "systemic console" free tool for fitting candidate planetary systems to radial velocity datasets. You can get this at I highly recommend it!

This is pretty cool. Without actually downloading the program, is there a link to a document that describes the actual algorithms they're using? From what I could glean from their blog, it could be anything from Expectation Maximization to Markov Chain Monte Carlo.



Posted by: Hungry4info Oct 22 2009, 12:33 PM

QUOTE (Greg Hullender @ Oct 21 2009, 08:26 PM) *
This is pretty cool. Without actually downloading the program, is there a link to a document that describes the actual algorithms they're using? From what I could glean from their blog, it could be anything from Expectation Maximization to Markov Chain Monte Carlo.
There's a paper describing Systemic in such level of detail here.

Posted by: Greg Hullender Oct 22 2009, 05:31 PM

QUOTE (Hungry4info @ Oct 22 2009, 04:33 AM) *
There's a paper describing Systemic in such level of detail here.

Excellent! Thank you very much!

This paper's a pretty good read, if you've got the math for it, and offers a very comprehensive answer to the original question. A point they mentioned that I hadn't thought about before is that they don't yet make relativistic corrections, which actually ought to matter considering how many of these planets are in very close orbits. It'll be fun to see what happens once they start to get their hands on the Kepler data.


Posted by: imipak Oct 23 2009, 06:47 PM

'Spherical cow' now has it's very own Wikipedia entry smile.gif

Posted by: PhilCo126 Dec 5 2009, 05:47 PM

Team of Astronomers using Japanese Subaru Telescope at Mauna Kea - Hawaii makes major discovery: GJ 758 B

Posted by: Hungry4info Dec 6 2009, 04:00 AM

I'm quite unsure as to why this is being made into such a big deal. The mass of the two objects are quite unconstrained (and in the case of c, it's not even known for sure if it's bound to the system). Even the minimum mass of 10 M_J for B is so high that it's hard to say for sure that this object would be a planet. Also, another object like this was imaged at 1RXS J160929.1-210524 with a mass of 8 M_J, but it's unknown if the object is bound to the system.

Posted by: centsworth_II Dec 6 2009, 07:15 AM

QUOTE (Hungry4info @ Dec 5 2009, 11:00 PM) *
I'm quite unsure as to why this is being made into such a big deal....
I'm not surprised that a site titled "News at Princeton" would make a big deal of any new discovery involving a Princeton scientist. How big a deal anyone else makes of it is up to them.

It is the first discovery of a new instrument and validates its usefulness in imaging sub-stellar objects orbiting stars. That seems pretty exciting to me. Isn't this just the second time such a feat has been accomplished?

Posted by: ngunn Dec 6 2009, 11:57 AM

On a different topic, I've not noticed discussion here of the planets/lithium anticorrelation announced a few weeks back.

Thinking about what could create a planetary system and also flush a star clean of lithium led me to the idea of a self-ejecting supernova companion. A little digging tracked that idea back 65 years to Fred Hoyle and it seems to have been seriously considered by at least some astronomers in the intervening time. It appears towards the end of this free sample page:

Any thoughts?

Posted by: Hungry4info Dec 6 2009, 02:26 PM

QUOTE ("centsworth_II")
Isn't this just the second time such a feat has been accomplished?

Maybe not the second, if you count 51 Sagittae B (first brown dwarf discovered around a sun-like star, in 2002, directly imaged) and 54 Piscium B (from 2006, also directly imaged). Spectral types G1V and K0V, respectively, with true masses of ~50 M_J for both objects. But I can see why such a high mass would cause these sub-stellar companions to be sort-of ignored. I guess it all depends on perspective. Epsilon Indi also has a pair of imaged brown dwarfs.


According to recent papers on the current theories, which the authors admit are incomplete, tidal interactions of a planet with its host star allow mixing of the stellar interior. This lets lithium descend deeper into the star than possible without the presence of a planetary companion. The lithium gets roasted alive and no longer shows up in stellar spectra.

The lithium anti-correlation is only applicable to a very narrow temperature range of about 100 K on either side of the temperature of Sol. M, K, F and A stars do not seem to have this trend (the population of planets around A stars is mostly inferred from the detection of planets around stars that have evolved and cooled to become cool giant stars, while too few planets are known to exist around OB stars).

Interestingly, sun-like stars with close stellar companions do not seem to have this anti-correlation. If stellar mixing is the cause, then one would expect stellar companions would do better at that than planetary companions. The orbits of close stellar companions are statistically indistinguishable from the orbits of planetary companions.

Another idea is that a star will magnetically interact with its protoplanetary disk and somehow allow the lithium to be transported deeper into the star and destroyed that way.

Posted by: ngunn Dec 6 2009, 04:57 PM

Yes I noticed the range of hypotheses offered, but they seem to focus on how A might cause B and sound a bit convoluted. I just think Hoyle's blast-your-neighbour-and-scram idea is more exciting, and it could neatly provide a single cause for both A and B.

QUOTE (Hungry4info @ Dec 6 2009, 02:26 PM) *
Interestingly, sun-like stars with close stellar companions do not seem to have this anti-correlation.

Well they wouldn't, would they? Their companions haven't exploded. smile.gif

Posted by: Hungry4info Dec 6 2009, 05:07 PM

Of course it's more exciting, but only in the "All stars are actually anti-matter/matter reaction driven" sort of sense. There's no reason to support it, and there's already other ideas that better explain what is observed.

Planet hosts are lithium poor. Planets not known to have stars are lithium rich.
(anti)correlation has something to do with planets (or planet formation).

This trend only shows up for stars within +/- 100 K of Sol's effective temperature.
(anti)correlation has something to do with the structures of stars +/- 100 K of Sol's effective temperature.

Even in our solar system, the planets (or the process of their formation) were able to cause Sol to become lithium poor. There is no evidence for any of our planets having exploded in the past.

Does the idea of a exploding companions explain why only near-stellar Teff stars display this correlation?
Does it explain why binary stars in the same temperature range do not?
Is there any evidence for planetary companions blasting their neighbors and screaming?

Consider the 16 Cygni system. Two sun-like stars: the lithium-poor star hosts a planet. The lithium-rich star hosts an M-dwarf.

Posted by: ngunn Dec 6 2009, 09:28 PM

QUOTE (Hungry4info @ Dec 6 2009, 05:07 PM) *
1 (anti)correlation has something to do with planets (or planet formation).

2 (anti)correlation has something to do with the structures of stars +/- 100 K of Sol's effective temperature.

3 There is no evidence for any of our planets having exploded in the past.

4 Is there any evidence for planetary companions blasting their neighbors and screaming?

1 - Agreed.
2 - Agreed.
3 - I didn't say that, and neither did Fred Hoyle. The explosion would have predated (and lead to) planet formation.
4 - I didn't say 'scream' either(!) I said scram, as in 'rapidly leave the area'.

There has also been quite a lot written over the years about the trauma to a close companion star when a supernova occurs, and about binaries becoming unbound following stellar explosions. I don't think it's far fetched to imagine that the trauma might involve lithium destruction for certain classes of star but not others.

16 Cygni B is around 1000AU from the AC pair, maybe far enough for a supernova to destroy the lithium in one but not the other.

There may be better theories as you say, but as you also say they are not complete and there is no clear winner yet so I don't think broader speculation is out of order at this stage.

Posted by: scalbers Jan 1 2010, 06:06 PM

I guess we can mention GJ1214b and the MEarth project in this thread...

Posted by: PhilCo126 Jan 9 2010, 09:59 AM

Keck telescopes on Mauna Kea - Hawaii discovered 2nd smallest exo-planet HD156668b at 80 light years in the constellation Hercules

Posted by: Mongo Jan 9 2010, 02:57 PM

I will charitably assume that the reporters left out the bolded part: 2nd smallest exoplanet discovered by radial velocity variations.

I count at least 5 smaller exoplanets, one of which was discovered by radial velocity variations.

Posted by: belleraphon1 Jan 9 2010, 08:06 PM

Agreed Mongo...

Go to Extrsolar Planets Encyclopedia catalog and sort by Mass you will find the three pulsar planets, MOA-2007-BLG-192-L-b (microlensing find) and GJ581e (the smaller of the RV finds).

Actually I think the discovery of GJ1214b is far more exciting. Close enough we can learn things about it's atmosphere from current space telescopes. GO MEarth team!!!


Posted by: ngunn Apr 14 2010, 10:59 AM

There is nothing like new data for shaking things up. smile.gif

Posted by: Ron Hobbs Jun 11 2010, 06:40 PM

The VLT has taken pictures of a planet orbiting beta Pic.

"For the first time, astronomers have been able to directly follow the motion of an exoplanet as it moves from one side of its host star to the other. The planet has the smallest orbit so far of all directly imaged exoplanets, lying almost as close to its parent star as Saturn is to the Sun. Scientists believe that it may have formed in a similar way to the giant planets in the Solar System. Because the star is so young, this discovery proves that gas giant planets can form within discs in only a few million years, a short time in cosmic terms."

I want to give a shout out to the folks at ESO; they provide some really cool graphics of their discoveries.

Posted by: remcook Jun 24 2010, 08:06 AM

Doing observations from the ground can have its advantages... smile.gif

Posted by: Drkskywxlt Jun 30 2010, 05:42 PM

Confirmation of the first directly imaged planet around a sun-like star thanks to Gemini. An 8Jup-mass planet at over 300AU!

Posted by: ustrax Nov 18 2010, 07:55 PM

It's extragalactastic! biggrin.gif

Posted by: ustrax Nov 19 2010, 11:09 PM

500! and 2... biggrin.gif
Wow! And to think that we just opened our eyes in 1988...what's ahead? smile.gif

Posted by: remcook Dec 2 2010, 09:14 AM

Well, finally that mysterious DPS presentation got cleared up
High density atmosphere or clouds on super-Earth GJ1214b

Posted by: ngunn May 19 2011, 04:14 PM

Free floating planets found by microlensing:

Food for WISE is probably out there. Go get 'em WISE!

Posted by: TheAnt Jun 19 2016, 09:49 AM

Some years ago we were given the impression that quite some stellar systems had hot Jupiters. That turned out to be an observational bias since such planets are easy to detect.
But such systems have been found again in quite a number in a study where HARPS were the main instrument though also Hubble and a few others were used.
It appear that in the open star cluster M67 about one out of

(Sorry for awakening this very old thread. But I were once asked by a moderator not to start to many new topics.)

Posted by: Explorer1 Aug 13 2016, 06:58 AM

A Proxima Centauri planet!? ohmy.gif
No official confirmation or denial, but an announcement set for the end of August (if true!).
Translated Der Spiegel article that has source:

Just hype, or something more?

Posted by: Gerald Aug 13 2016, 07:46 AM

Seems, they found a hint to a small deviation of Proxima Centauri's trajectory close to the limits of statistical evidence.
The press tends to make a sensation of exciting preliminary hypotheses. So, let's wait, how statistically significant the findings actually turn out to be.

Posted by: HSchirmer Aug 14 2016, 01:30 AM

Just noticed that Der Spiegel and other online sources are reporting a pre-announcement about a
a terrestrial planet with liquid water around alpha centauri...

Anybody hearing anything?

Posted by: JRehling Aug 14 2016, 02:32 AM

Google searches limited to the last week show several results; this is one:

It is Proxima Centauri that is the host star; Proxima Centauri is believed to be part of the Alpha Centauri system, but it is quite remote from the other two and it is not certain that they are gravitationally bound. However, their distance from us is nearly equal.

Any discovery like this would be very exciting, but I'm quite sure that at this point, the only thing anyone could say about liquid water would be speculation based on the amount of insolation a planet receives; actually detecting liquid water would be a much harder feat.

I should say that Kepler data indicate that very roughly 8% of red dwarfs have Earth-sized planets in their habitable zone and roughly 8% have a Super Earth in their habitable zone… obviously this depends on definitions of HZ and the size bounds used. With a looser definition, the sum of those probabilities plus Mars-sized planets might climb over 50%. Which is to say: Without making any observations of Proxima Centauri, one could already saw that there's a good chance of a terrestrial planet with temperatures that could permit liquid water. One might even say that it's probable for each red dwarf. (Although this packs a lot of uncertainty into the "could permit liquid water" and definition of "terrestrial planet.") Furthermore, it seems nearly certain that one of the four or so closest red dwarfs should have a planet that meets those loose definitions.

I'll be eager to hear more, though. Proxima Centauri is the absolute easiest star in the universe for follow-up science on its planetary system. It would be a nice bit of luck if a candidate "earthlike" planet were there.

Posted by: nprev Aug 14 2016, 07:41 AM

MOD MODE: Merged topic created for this alleged Proxima planet into this topic. There is absolutely no way that liquid water could have possibly been detected on this purported planet via the espoused (ground-based) discovery method. Media reports are spinning rapidly out of control. The characterization 'Earth-like" is inherently misleading; "Earth-sized" is much more plausible and accurate.

Furthermore, this is the same team that 'discovered' Alpha Centauri Bb, which was subsequently not confirmed. All these points should produce some healthy skepticism.

Bottom line is that this story is extremely speculative at this point--and therefore of extremely questionable quality as subject matter for UMSF. Discussion will be allowed using reputably sourced information, but not obvious sensationalism as seems to be the case for this thus far. This thread will be closed immediately if the discussion does not meet Forum standards.

"Extraordinary claims require extraordinary evidence"- Sagan's Law

Posted by: JRehling Aug 14 2016, 03:01 PM

This is indeed a good time to invoke Sagan's Law.

The notion that Proxima Centauri might have a planet is not a wild one at all – in fact, it may be nearly certain that any given red dwarf have at least one planet. The remarkable claim is about how much it might be like Earth, and those words "might" and "like" are packed full of opportunities to be vague and say nothing meaningful.

Here are key statements from the Spiegel article:

• The research involved in this took place at the limit of what measurements technically feasible.
• The method used involved "variations in the motion of the star."

The second statement is ambiguous. The Doppler method that measures radial (towards or away from Earth) movement of the star has been one of the two most productive methods for discovering exoplanets. Another method – long-discussed, but never-yet successful – has been to look at how a star wobbles side-to-side. The Doppler method works equally well for stars that are far or near, whereas the wobble method would be more successful for close stars – and Proxima Centauri is the closest – than any other. The Doppler method is also blind to planets in orbits that we see face-on, whereas the wobble method would work just fine for those… if it works for any cases at all, which is not clear. Finding Earth-mass planets has been elusive even for the Doppler method, with the smallest so far confirmed having a mass of about 3.7 mass[Earth] with an uncertainty of about 0.7. When the uncertainty in one of the best cases is 0.7 mass[Earth], it gives you an idea of the hopelessness of determining that any subsequent discovery would be very close to 1.0 mass[Earth] without very large relative uncertainty.

The first statement is of paramount importance: If the results come at the limit of what is technically feasible, then they almost inherently contain uncertainty, which would mean that there could be doubt as to whether or not they detected a planet as opposed to noise, and if they did detect a planet, even if it happened to be very much Earth-sized and getting Earth-like amounts of sunlight, the measurements would have too large of an error for us to be confident about the nature of the planet yet.

Given what we know in general about exoplanet occurrence, it would be surprising if Proxima Centauri didn't have some planets smaller than Neptune orbiting it, and it wouldn't be surprising if it had one about the size of Earth and getting about that much sunlight… but "not surprising" is a long way from confirmed.

Posted by: Explorer1 Aug 14 2016, 04:18 PM

Presumably they wouldn't have published the article if they knew they would be embarrassed by another false positive, right? The lack of flat denial from ESO also makes me anticipate that there really will be some announcement by the end of the month. Then we'll see where the chips fall, and the next step of the scientific method (attempts to replicate/confirm results) can be put in practice.

Posted by: Gerald Aug 14 2016, 11:12 PM, and
But at the same time


." ESO-Sprecher Richard Hook erklärte jedoch zu dem angeblichen Sensationsfund, die Angaben basierten offenbar "größtenteils auf Gerüchten". Er könne den Inhalt des "Spiegel"-Berichts "nicht bestätigen". Die Ergebnisse der Suche nach einem möglichen Planeten bei Proxima Centauri würden "zur rechten Zeit bekanntgegeben", betonte Hook.

ESO-speaker Richard Hook, however, explained regarding the presumed sensational findings, the statements are obviously based "mostly on rumors". He "can't confirm" the contents of the "Spiegel" report. The results of the search for a possible planet near Proxima Centauri will be "reported in due time", emphasized Hook.

Posted by: nprev Aug 14 2016, 11:35 PM

Thanks, Gerald. That's the kind of clarifying information that's needed concerning this story at this point.

Posted by: alphasam Aug 18 2016, 07:09 PM

I'll just leave this here cool.gif

From BBC The Sky at Night presenter Chris Lintott;

Posted by: JRehling Aug 19 2016, 06:23 PM

Der Spiegel has published a new article that almost looks like the previous rumor-level article but with slightly less hedging:

It'll be nice to have absolute confirmation that Proxima Centauri has planets but, to recap, it is somewhere between expected and very likely for any given red dwarf to have planets, and because they tend to have small planets, it is more or less expected for it to have a planet that's roughly earth-sized.

What would be nice to know is what uncertainty exists concerning any such detection. If the result is a detection with an estimated radius between 0.5 and 2.5 Earth radii, and/or similar uncertainty regarding its illumination, that's not going to mean much.

It would also be great, and surprising, if Proxima Centauri's planetary plane is aligned such that we see its planets transit, but there's no indication that this is going to be part of the announcement.

If Der Spiegel is accurate, we'll know within a couple of weeks what the team has found.

Posted by: alphasam Aug 22 2016, 02:14 PM

There will be a press conference at ESO headquarters this Wednesday at 1pm CET, 7am EDT.

Posted by: TheAnt Aug 23 2016, 06:26 PM

Hmm, if Der Spiegel is to believed, it is now claimed that the source was from the PaleRedDot team after all.
Lets see about this ESO announcement tomorrow. =)

Posted by: Gerald Aug 24 2016, 11:46 AM

Dear friends we will be making an announcement today at 19:00 CEST. Please stay tuned until then

Posted by: alphasam Aug 24 2016, 11:52 AM

Yeah, there is a conference with the press going on now but not being broadcast :-( , the end of the embargo has been set for the evening.

Posted by: DEChengst Aug 24 2016, 05:04 PM

ESOcast 87: Pale Red Dot Results:

Mass is at least 1.3 Earth masses and the orbital period is 11.2 days.

And the actual press briefing that was given earlier this afternoon.

Posted by: TheAnt Aug 24 2016, 05:15 PM

Here we got the full facts, a 'year' lasting 11 days, that's a tight orbit for the Proxima C planet

Edit, adding resources that popped up after the embargo was lifted:

The Icecat page The habitability of Proxima Centauri b

Posted by: Gladstoner Aug 24 2016, 07:49 PM

FYI, Centauri Dreams is a good resource for exoplanets as well as general interstellar exploration topics:

Posted by: JRehling Aug 25 2016, 12:59 AM

This work contains, also, an interesting hint of the cup-half-empty: The detection of this planet and not any other apparent signal that interferes appreciably with it says something about a lack of other planets within certain parameters. There must be no planet that is closer to Proxima Centauri and more than a fraction of the mass of Proxima b, nor any planet a bit further out and a few times more massive. This is interesting because, a priori, there could be space for another terrestrial planet with prospects for liquid water on the surface. Proxima Centauri may still – and very likely does – have other planets, but this work places bounds on their size and orbits.

Hopefully, we'll soon get some information on the systems of Alpha Centauri A and Alpha Centauri B. Planets with earthlike temperatures would have much longer orbital periods than 11 days (more like 150 to 500 days) and so much longer studies will be needed. On the plus side, planets orbiting one of those could be observed directly a bit more easily, using a chronograph to block a star that is 0.4 to 1.1 AU away from the planet, which is easier due to the larger angular separation than blocking Proxima Centauri to observe Proxima b.

Posted by: Mongo Aug 25 2016, 01:46 AM

We present a study of 4 different formation scenarios that may explain the origin of the recently announced planet `Proxima b' orbiting the star Proxima Centauri. The aim is to examine how the formation scenarios differ in their predictions for the multiplicity of the Proxima planetary system, the water/volatile content of Proxima b and its eccentricity, so that these can be tested by future observations. A scenario of in situ formation via giant impacts from a locally enhanced disc of planetary embryos and planetesimals, predicts that Proxima b will be a member of a multiplanet system with a measurably finite value of orbital eccentricity. Assuming that the local solid enhancement needed to form a Proxima b analogue with a minimum mass of 1.3 Earth masses arises because of the inwards drift of solids in the form of small planetesimals/boulders, this scenario also likely results in Proxima b analogues that are moderately endowed with water/volatiles, arising from the dynamical diffusion of icy planetesimals from beyond the snowline during planetary assembly. A scenario in which multiple embryos form, migrate and mutually collide within a gaseous protoplanetary disc also results in Proxima b being a member of a multiple system, but where its members are Ocean planets due to accretion occurring mainly outside of the snowline, possibly within mean motion resonances. A scenario in which a single accreting embryo forms at large distance from the star, and migrates inwards while accreting either planetesimals/pebbles results in Proxima b being an isolated Ocean planet on a circular orbit. A scenario in which Proxima b formed via pebble accretion interior to the snowline produces a dry planet on a circular orbit. Future observations that characterise the physical/orbital properties of Proxima b, and the multiplicity of the system, will provide valuable insight into its formation history.

We analyze the evolution of the potentially habitable planet Proxima Centauri b to identify environmental factors that affect its long-term habitability. We consider physical processes acting on size scales ranging between the galactic scale, the scale of the stellar system, and the scale of the planet's core. We find that there is a significant probability that Proxima Centauri has had encounters with its companion stars, Alpha Centauri A and B, that are close enough to destabilize Proxima Centauri's planetary system. If the system has an additional planet, as suggested by the discovery data, then it may perturb planet b's eccentricity and inclination, possibly driving those parameters to non-zero values, even in the presence of strong tidal damping. We also model the internal evolution of the planet, evaluating the roles of different radiogenic abundances and tidal heating and find that a planet with chondritic abundance may not generate a magnetic field, but all other models do maintain a magnetic field. We find that if planet b formed in situ, then it experienced ~160 million years in a runaway greenhouse as the star contracted during its formation. This early phase may have permanently desiccated the planet and/or produced a large abiotic oxygen atmosphere. On the other hand, if Proxima Centauri b formed with a thin hydrogen atmosphere (<1% of the planet's mass), then this envelope could have shielded the water long enough for it to be retained before being blown off itself. Through modeling a wide range of Proxima b's evolutionary processes we identify pathways for planet b to be habitable and conclude that water retention is the biggest obstacle for planet b's habitability. These results are all obtained with a new software package called VPLANET.

Proxima b is a planet with a minimum mass of 1.3 MEarth orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass, active star and the Sun's closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time evolution of the star's spectrum, which is essential for modeling the flux received over Proxima b's lifetime. We also show that Proxima b's obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet's eccentricity and level of triaxiality. Next we consider the evolution of Proxima b's water inventory. We use our spectral energy distribution to compute the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find that Proxima b is likely to have lost less than an Earth ocean's worth of hydrogen before it reached the HZ 100-200 Myr after its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We conclude that Proxima b is a viable candidate habitable planet.

Radial velocity monitoring has found the signature of a Msini=1.3~M⊕ planet located within the Habitable Zone of Proxima Centauri, (Anglada-Escud\'e et al. 2016). Despite a hotter past and an active host star the planet Proxima~b could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016).

Here we use a 3D Global Climate Model to simulate Proxima b's atmosphere and water cycle for its two likely rotation modes (1:1 and 3:2 resonances) while varying the unconstrained surface water inventory and atmospheric greenhouse effect.

We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water inventory larger than 0.6 Earth ocean, liquid water is always present, at least in the substellar region. Liquid water covers the whole planet for CO2 partial pressures ≳1~bar. For smaller water inventories, water can be trapped on the night side, forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2 pressure is required to avoid falling into a completely frozen snowball state if water is abundant. If the planet is dryer, ∼0.5~bar of CO2 would suffice to prevent the trapping of any arbitrary small water inventory into polar ice caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes discussed here.

We use our GCM to produce reflection/emission spectra and phase curves. We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular separation of 7λ/D at 1~μm (with the E-ELT) and a contrast of ∼10−7. The magnitude of the planet will allow for high-resolution spectroscopy and the search for molecular signatures.

Posted by: JRehling Aug 25 2016, 04:08 AM

An important result, discussed in more detail in the Turbet, et al. paper that Mongo has linked, is that Proxima b will be directly observable and possible to analyze spectrally, using the E-ELT and possibly JWST. Generally speaking, the small separation between HZ planets around M dwarfs will make this impossible for systems located >20 light years away, but we hit the jackpot by getting one at 4.2 light years away, which makes it possible. Other candidate exoplanets that fit the bill for this kind of observation include Kapetyn b (13 light years) and Tau Ceti e (12 light years). The best possible candidates would be any such planets that might exist around Alpha Centauri A or B, which would have a much larger separation from their stars than Proxima b.

So, direct observations may begin in 2019 (JWST) or 2024 (E-ELT), with at least two candidate HZ terrestrial planets to observe, and perhaps many more as the search for more planets continues.

Posted by: Mongo Aug 26 2016, 12:26 AM

Proxima Centauri b, an Earth-size planet in the habitable zone of our nearest stellar neighbour, has just been discovered. A theoretical framework of synchronously rotating planets, in which the risk of a runaway greenhouse on the sunlight side and atmospheric collapse on the reverse side are mutually ameliorated via heat transport is discussed. This is developed via simple (tutorial) models of the climate. These show that lower incident stellar flux means that less heat transport, so less atmospheric mass, is required. The incident stellar flux at Proxima Centauri b is indeed low, which may help enhance habitability if it has suffered some atmospheric loss or began with a low volatile inventory.

Posted by: Mongo Aug 29 2016, 01:33 AM

The newly detected Earth-mass planet in the habitable zone of Proxima Centauri could potentially host life - if it has an atmosphere that supports surface liquid water. We show that thermal phase curve observations with the James Webb Space Telescope (JWST) from 5-12 microns can be used to test the existence of such an atmosphere. We predict the thermal variation for a bare rock versus a planet with 35% heat redistribution to the nightside and show that a JWST phase curve measurement can distinguish between these cases at 5σ confidence. We also consider the case of an Earth-like atmosphere, and find that the ozone 9.8 micron band could be detected with longer integration times (a few months). We conclude that JWST observations have the potential to put the first constraints on the possibility of life around the nearest star to the Solar System.

Posted by: Holder of the Two Leashes Aug 29 2016, 05:53 PM

QUOTE (Mongo @ Aug 28 2016, 07:33 PM) *
...the ozone 9.8 micron band could be detected with longer integration times (a few months).

The paper itself mentions 60 days of integration. That's an awful lot of dedicated time on the JWST to ask for.

Posted by: JRehling Aug 30 2016, 06:34 PM

I think JWST will be able to study planets in the HZ of nearby G and K stars, but not M dwarfs except for the very closest ones, where the possibility is marginal, and – as you say – very resource-intensive. On the other hand, JWST may be able to do some interesting studies of Proxima b that are less expensive, like directly measuring the temperature.

The Giant Magellan Telescope will have an angular separation similar to JWST, and will probably be useful for more or less the same systems. However, E-ELT will have distinctly better resolution and will be the "killer app" for nearby exoplanet studies.

JWST will give us our first followup studies of the HZ exoplanets with the widest angular separation, such as (the unconfirmed) Tau Ceti e. That may be a very small set. E-ELT will be the next major advance. Then we'll probably have to wait for a new space-based telescope designed for the task to improve on that.

Posted by: katodomo Aug 31 2016, 06:21 PM

As an overall strategy, JWST is more of an intermediate and supplanting step:

On the European side, PLATO is supposed to launch around the same time that E-ELT becomes active (and around the same time GAIA's catalogue gets published), which will probably make a great pair in space-based detection and first characterization and then ground followup observation throughout the second half of the 2020s.

The US side similarly works with TMT and the still only proposed WFIRST and ATLAST missions in the same timeframe.

Posted by: ZLD Sep 1 2016, 02:18 AM

Not getting my hopes up for TMT anymore. While only a little over half the light gathering ability, the Giant Magellan is trucking right along though and is supposed to be done in less than 5 years from now.

Posted by: Mongo Sep 13 2016, 01:10 AM

This one is interesting, it considers what can be accomplished with the existing ESO VLT observatory with feasible upgrades to operational (SPHERE) and under-construction (EXPRESSO) instruments:

Context. The temperate Earth-mass planet Proxima b is the closest exoplanet to Earth and represents what may be our best ever opportunity to search for life outside the Solar System.

Aims. We aim at directly detecting Proxima b and characterizing its atmosphere by spatially resolving the planet and obtaining high-resolution reflected-light spectra.

Methods. We propose to develop a coupling interface between the SPHERE high-contrast imager and the new ESPRESSO spectrograph, both installed at ESO VLT. The angular separation of 37 mas between Proxima b and its host star requires the use of visible wavelengths to spatially resolve the planet on a 8.2-m telescope. At an estimated planet-to-star contrast of ~10^-7 in reflected light, Proxima b is extremely challenging to detect with SPHERE alone. The use of the high-contrast/high-resolution technique can overcome present limitations by combining a ~10^3-10^4 contrast enhancement from SPHERE to a ~10^4 gain from ESPRESSO.

Results. We find that significant but realistic upgrades to SPHERE and ESPRESSO would enable a 5-sigma detection of the planet and yield a measurement of its true mass and albedo in 20-40 nights of telescope time, assuming an Earth-like atmospheric composition. Moreover, it will be possible to probe the O2 bands at 627, 686 and 760 nm, the water vapour band at 717 nm, and the methane band at 715 nm. In particular, a 3.6-sigma detection of O2 could be made in about 60 nights of telescope time. Those would need to be spread over 3 years considering optimal observability conditions for the planet.

Conclusions. The very existence of Proxima b and the SPHERE-ESPRESSO synergy represent a unique opportunity to detect biosignatures on an exoplanet in the near future. It is also a crucial pathfinder experiment for the development of Extremely Large Telescopes and their instruments (abridged).

From the paper's conclusions:

– We find that the reflected spectrum from Proxima b can be detected at the 5- level in 20-40 nights of telescope time for a contrast enhancement factor K = 3000 (SPHERE+) and a planet-to-star flux ratio of 1.0-1.4 x 10^7 (Earth-like atmospheres). This includes a measurement of the planet true mass (as opposed to minimum mass) and orbital inclination, and the measurement of its broadband albedo.

– We find that O2 can be detected at the 3.6- level in about 60 nights of observing time at K = 5000, for a planet-to-star contrast of 1.4 x 10^7. Those nights would need to be spread over 3 years to guarantee optimal observability conditions of the planet and sucient separation between telluric and planetary O2 lines.

– We also show that H2O can be probed in a similar amount of telescope time provided the H2O column density is similar to wet regions of Earth.

– Finally, it is likely that CH4 is detectable as well if its column density is similar to or larger than the one seen in Jupiter and Saturn, although we could not address this point quantitatively.

In conclusion, while we do not underestimate the technical challenges of our proposed approach, we do believe that SPHERE+ESPRESSO is competitive for becoming the first instrument to characterize a habitable planet.

Posted by: Explorer1 Feb 21 2017, 08:03 PM

Press conference tomorrow on a new discovery, experts of exoplanet atmospheres involved: has some good guesswork of what it may be...

Posted by: nprev Feb 22 2017, 01:50 AM

Reminder to all: We do not discuss embargoed information here; always wait until the official release. Thanks! smile.gif

Posted by: hendric Feb 22 2017, 06:16 PM

Posted by: HSchirmer Feb 22 2017, 06:57 PM

QUOTE (hendric @ Feb 22 2017, 06:16 PM) *

Posted by: JRehling Feb 22 2017, 08:06 PM

This is quite an interesting and – IMO – surprising discovery for the sheer number of planets packed so tightly together. Six of the planets have orbital periods between 1.51 and 12.35 days. Not surprisingly, there are small-integer ratios galore between orbital periods. In terms of the shortest period, the next four are 8:5, 8:3, 4:1, and 6:1.

In terms of bolometric luminosity, the second, third, and fourth ones get about the same thermal input as Venus, Earth, and Mars. There's no doubt that whatever one considers to be earthlike context in terms of that alone, at least one of these planets has it.

And here's one of the interesting consequences: There are about 500 red dwarfs closer than this system. The probability of a transit for a single planet in the "habitable zone" of such stars is about 2.5%, which would mean 12.5 such systems. But if there are multiple planets per system, then the number of planets we can see transiting will be higher than ~12.5, perhaps double that. And that'll increase the bounty when the time comes that we can do serious follow-up science by examining spectra.

A decade or so from now, we may have spectra for something like 20-50 sub-Neptune-sized planets in the HZ of red dwarfs. That's a nice future set of results to look forward to.

Posted by: ngunn Feb 22 2017, 09:03 PM

QUOTE (JRehling @ Feb 22 2017, 08:06 PM) *
Not surprisingly, there are small-integer ratios galore between orbital periods.

And, if the Jovian system is anything to go by, these resonances will be evolving over time with each planet experiencing different episodes of orbital forcing, eccentricity change and tidal heating. So once the orbital/thermal history of the Galilean moons has been definitively settled the dynamicists will then have this diabolically complex and even more crowded planetary system to chew over.

Another curiosity is that the system lies within one degree of our ecliptic plane. Does this mean that seen from there our Sun would also exhibit planetary transits?

Posted by: JRehling Feb 22 2017, 09:36 PM

QUOTE (ngunn @ Feb 22 2017, 02:03 PM) *
Another curiosity is that the system lies within one degree of our ecliptic plane. Does this mean that seen from there our Sun would also exhibit planetary transits?

Maybe. The ecliptic is the plane of Earth's orbit, and 1° would put the Earth almost 4 Sun radii above/below the Sun's disk as seen from afar. But the other planets are all separate players, so perhaps some of them happen to transit as seen from Trappist 1. The farther out you go, the less likely. Also note that close-in planets tend to orbit close to the star's plane of rotation, whereas planets further out tend to orbit in planes that are closer to one another than to the star's rotation. These are the things we've learned from other planetary systems. So if I had to bet, I'd bet that none of the solar system's planets transit as seen from Trappist 1. (A couple of pages of trigonometry could provide the answer.)

Roughly speaking, the probability of a planet orbiting a sunlike star at 1.0 AU transiting its star is 0.5%. Red dwarfs are smaller than the Sun but their, e.g., "habitable zone" is much closer in by an even larger factor, so planets orbiting red dwarfs and getting the same radiation as Earth have about a 2.5% probability of transiting. This – along with the intrinsic number of different types of stars – is why, when we get instruments that can detect the spectra of transiting HZ terrestrial planets, we should get a bonanza of red dwarf candidates vs. far fewer that orbit sunlike stars.

As seen from another system, the two most easily detectible planets in our solar system are Jupiter and Venus. Venus, because it is relatively large and relatively likely to transit the Sun; Jupiter, because its gravity would tug the Sun significantly for the Doppler method. Earth and Saturn are the next runners-up. Detecting Mercury would require the Sun to exhibit very low noise. Mars is a distant sixth. We have yet to have any methods that have much chance of detecting Uranus/Neptune analogs, though with microlensing, it's a longshot.

Posted by: ngunn Feb 22 2017, 10:52 PM

QUOTE (JRehling @ Feb 22 2017, 09:36 PM) *
the two most easily detectible planets in our solar system are Jupiter and Venus. Venus, because it is relatively large and relatively likely to transit the Sun; Jupiter, because its gravity would tug the Sun significantly for the Doppler method.

So in Trappist-1 we have detected the 'Venuses', but its 'Jupiters', if any, presumably would not transit but await discovery by longer term observation of the system for slow wobbles.

Posted by: JRehling Feb 23 2017, 05:41 AM

QUOTE (ngunn @ Feb 22 2017, 03:52 PM) *
So in Trappist-1 we have detected the 'Venuses', but its 'Jupiters', if any, presumably would not transit but await discovery by longer term observation of the system for slow wobbles.

We don't know a lot about the outer systems of red dwarfs. In a case like this, the outer system may be empty, may have more terrestrial planets, or may have some bigger planets. Generally, red dwarfs have far fewer big planets than do solar-type stars, so it's quite plausible that there simply aren't any Jupiters.

There are many unknowns in exoplanet frequency concerning the norms of system architecture. We know quite well what the inner systems look like in terms of planet frequency by type (size and orbital period), but we don't have a lot of firm evidence about the dependencies, i.e.., if there is a planet of type X, how likely is it that the system also has a planet of type Y? In fact, I think it's rather challenging even to describe systematically these sorts of dependencies. It's troublingly verbose even if we use bins and talk about systems with multiple planets (e.g., if we have a Super Earth orbiting between 30 and 45 days and a Neptune orbiting between 60 and 90 days, then what is the probability of each size of planet with a period between 120 and 240 days?). But, because any such bins are arbitrary, I think the whole topic seems almost maddeningly complex.

Posted by: nprev Feb 23 2017, 05:54 AM

ADMIN NOTE: All TRAPPIST-1 posts have been moved here from "Exoplanet Atmospheres." Please carry on; thanks! smile.gif

Posted by: TheAnt Feb 23 2017, 12:41 PM

QUOTE (JRehling @ Feb 23 2017, 06:41 AM) *
..... I think the whole topic seems almost maddeningly complex.

It is complex indeed!
3 planets in the habitable zone, but will any of them turn out to be even close to that considering other conditions that just temperature?
It looks from the summary of this paper that they have tried to figure out if the planets might be habitable at all considering the very strong

Press release from the horse's mouth, ESO

Posted by: hendric Feb 23 2017, 05:24 PM

QUOTE (JRehling @ Feb 22 2017, 11:41 PM) *
But, because any such bins are arbitrary, I think the whole topic seems almost maddeningly complex.

Yeah, we have to be very very careful when we do datamining for correlations. I'm reading Standard Deviations by Gary Smith, and that's one of the big dangers to look out for when attempting to discuss data with many possible combinations. Even random data will have a few correlations if it's sliced and diced enough different ways. Experimental physics gets around this issue by doing calculations and flow development on a small subset of the data, and once a signal is detected, rerunning the analysis across the whole dataset.


Posted by: JRehling Feb 23 2017, 06:15 PM

The big reason why it is much easier to determine planet frequency for a given bin (size, period) than to determine the norms of system architecture is that the norms of orbital inclinations are unknown (and sure to vary from case to case).

When we search a star for 1 transiting planet, we know that the orientation of the putative planet's orbit to our line of sight is a random variable, and we can thereby take the number of detections and compensate for that random variable, which is very neatly described in terms of simple geometry.

But when we try to determine the frequency of pairs (of whatever types), the neatness falls apart and we have chaos, simply because we don't know what the probability is of a second planet transiting given that a first planet did. Clearly, these are not independent variables, but the degree of dependence is unknown. Compensating for the geometric variations is highly sensitive to what the norms are: If we knew that an inner planet's orbital inclination vs. the outer planet has a standard deviation of, say, 1°, then we would know precisely how much to compensate for the geometric factors and convert our observations into frequency measures. But if it's actually 1.5°, then our estimate is off by 50%. And to make this wildly complex, the relationship is sure to be a very complex function of the sizes of the planets, not only because of the dynamics of how their orbits evolved, but in how the system evolved during accretion.

It's possible to resolve this, eventually, by measuring the orbital inclinations between pairs, which can be done by measuring the duration of transits, but this requires a lot of data, because in any particular instance, two planets could both transit their star even if their orbits are highly inclined because the line where their planes cross could happen to go right through the star.

Even then, different stellar populations may be different in this regard, and large surveys will probably be biased in uncontrollable ways. For example, Kepler looked off the galactic plane, which ends up being a significant bias because metallicity varies with galactic latitude, and the formation of large planets correlates with metallicity!

Possibly the killer technology to end all of this horrible ambiguity will be when we can visually resolve planets orbiting solar-type stars at >0.5 AU. Then we will simply see whole systems and definitive data on orbital inclination dependence will come in in a rush.

Posted by: fredk Feb 23 2017, 07:23 PM

QUOTE (JRehling @ Feb 22 2017, 10:36 PM) *
1° would put the Earth almost 4 Sun radii above/below the Sun's disk as seen from afar.

I find an ecliptic latitude of close to 38' for this star. For earth transits to be visible from the star, it'd have to be within about 1/4 deg of the ecliptic. So earth transits are definitely out.

Posted by: ngunn Feb 23 2017, 07:38 PM

When will we know we have fathomed the'norms of system architecture'? I'd say: when nature is no longer able to surprise us.

Not so very long ago people were willing to make general statements to the effect that other planetary systems, if they existed at all, would probably be much like our own. It seems to me the main thing we've learned since then is just how far we are from knowing the full scope of possibilities. It's not only hard parameters like system geometry, instrumental limitations and the like which cause biased data sets. There's a human contribution too because premature generalisation can all too easily limit what one chooses to go looking for. Now that one is going to be really hard to quantify.

EDIT - Fred I was going from this map when I estimated 1 degree:

Posted by: hendric Feb 23 2017, 08:27 PM

If I am reading the Simbad entry correct for Trappist 1

then it has a high proper motion with a -471 mas change in declination per year. I am handwaving the difference between the ecliptic and the celestial equator because I can. smile.gif

Given fredk's numbers of 38-15 = 23 arc minutes away from ecliptic, or 1380 arc seconds.

1380/.471 ~= 3000 years

So TRAPPIST-1 will be able to observe Earth transits a few thousand years from now.

The rest of the planets are inclined > 3/4* to the ecliptic, so unless they just happened to cross near TRAPPIST-1, they won't cause transits.

Posted by: fredk Feb 23 2017, 09:33 PM

Looks good, Hendric. (But that's 23' from the sun's limb.)

Taking into account the RA proper motion only helps, since it's eastward, ie towards the ecliptic. So it might only take a couple of thousand years...

Posted by: ngunn Feb 23 2017, 11:33 PM

Brilliant stuff guys, thanks for taking an interest in a casual question. It has set me off thnking though about the invariable plane of the solar system. All the planetary orbits must eventually relate to that as they evolve over time but I can't find it plotted on a star map as the ecliptic and galactic equator commonly are. Can anybody help?

Posted by: Explorer1 Feb 24 2017, 12:33 AM

It's possible to resolve this, eventually, by measuring the orbital inclinations between pairs, which can be done by measuring the duration of transits, but this requires a lot of data, because in any particular instance, two planets could both transit their star even if their orbits are highly inclined because the line where their planes cross could happen to go right through the star.

Wouldn't direct imaging also work (i.e. a starshade)?

Posted by: JRehling Feb 24 2017, 02:38 AM

QUOTE (Explorer1 @ Feb 23 2017, 05:33 PM) *
Wouldn't direct imaging also work (i.e. a starshade)?

Yes, I got to that at the end of the post… "visually resolve…"

One should note, though, that when we will be able to resolve certain cases, many others will remain unresolved, and something like the orbits around Trappist 1 are a tall order – these are on the order of 0.02 AU and are located 39 light years away. This is about 1/400th the angular size of a 1-AU orbit around Alpha Centauri! It seems quite likely that a whole generation (or several) of technological advances will be needed to go from the one to the other… and we're nowhere near able to achieve the easier of those two cases yet or in the foreseeable future.

Posted by: TheAnt Feb 24 2017, 08:17 AM

QUOTE (JRehling @ Feb 24 2017, 03:38 AM) *
.....something like the orbits around Trappist 1 are a tall order – these are on the order of 0.02 AU and are located 39 light years away. This is about 1/400th the angular size of a 1-AU orbit around Alpha Centauri!

Yes I thought so too, yet thank you for giving it in straight numbers JRehling.
With all orbits closer than Mercury and almost as tight as the moons around Jupiter, I had the gut feeling that taking direct images would be near impossible.
The good thing about these transiting planets is that we should be able to get a good idea of the makeup of the atmospheres of these planets - or lack thereof.

Posted by: hendric Feb 24 2017, 05:33 PM

In a related Nova episode on the Origami Revolution, they demonstrate how a starshade could deploy for a future exoplanet telescope mission.

Posted by: scalbers Feb 25 2017, 12:47 AM

For visually resolving I remain a fan of the old Planet Imager (PI) mission concept, a network of space interferometers spread over thousands of kilometers. Each interferometer in the network is a Terrestrial Planet Finder (TPF) with several telescopes on the order of meters or a few kilometers from each other. The TPF link below is simply to the smaller nested interferometer element.

Posted by: JRehling Feb 25 2017, 10:45 PM

QUOTE (TheAnt @ Feb 24 2017, 01:17 AM) *
Yes I thought so too, yet thank you for giving it in straight numbers JRehling.

To clarify further:

The JWST, 39-meter E-ELT and other future telescopes will be able to resolve exoplanet systems well enough that a planet at 1 AU and its star will be in different pixels. It is an open question, however, whether the point spread function will be adequate to allow spectroscopy that can identify the presence of atmospheric components, and this is a function of many unknowns, both in the instrument and in the universe itself. The best hope is for solar-like stars (or even bigger/hotter ones) that are particularly nearby (e.g., less than 30 light years). The problem is that there aren't that many solar-like stars within 30 light years – about 20 class G stars. If 10% of them have an earth-sized planet in the habitable zone, we're talking about very few cases – plausibly zero!

Red dwarfs will have their habitable zones in closer, which makes it absolutely impossible to get the planet and star in different pixels with planned instruments. However, there are a lot more of them and a much higher probability of planets that transit. So what we count on here is to examine the spectra of planets when they transit and/or are eclipsed. Moreover, the star is much less bright than the planet.

So, there are factors that favor the solar-like case and factors that favor the red dwarf case and these will be, to some extent, two complementary branches of exploration. The red dwarf case is probably going to be more productive over the next few decades because studies based on sheer light gathering do not require good resolution and we could conceivably build huge light-bucket telescopes for these studies. But, one final problem with the red dwarf case – we don't even know if the kinds of planets that we hope to find are capable of existing in red dwarf systems. Suppose that tidal locking means no magnetic field – then the planets may lose their H2O and go the path of Venus or something equally dead.

I suppose that mass light gathering is going to work better than superior resolving power – it involves fewer unknowns, and scales better to systems that are further away, whereas increased distance is inherently problematic for efforts to resolve planets. Given enough light gathering, we could – in principle – generate light curves that show the presence of different surface units, oceans and continents, etc.

For any and all of the above, nature has to cooperate. I think one of the terrible problems that we'll encounter will be clouds. For some fraction of the interesting worlds we find, clouds will block our view of the surface and lower atmosphere, and we'll be in the same situation that we were in with Venus in 1950, but with no way for probes or radar to solve the problem for us.

Posted by: ZLD Feb 26 2017, 03:00 PM

QUOTE (scalbers @ Feb 24 2017, 06:47 PM) *
For visually resolving I remain a fan of the old Planet Imager (PI) ...

Same here. Interferometers offer the best ROI for visual observations. One change to their proposal I always wished for was the capability to add more telescopes to the constellation in the future. And also a pre-planned robotic servicing craft that could be sent to refuel them. One can only dream I suppose. rolleyes.gif

Posted by: Julius Feb 26 2017, 08:10 PM

[quote name='JRehling' date='Feb 25 2017, 11:45
Suppose that tidal locking means no magnetic field – then the planets may lose their H2O and go the path of Venus or something equally dead.

Could you explain more why tidal locking means no magnetic field?

Posted by: Hungry4info Feb 26 2017, 08:44 PM

The default assumption is the slower rotation periods will make it harder for planets to generate magnetic fields, but this is still a topic of ongoing research.

Posted by: fredk Feb 26 2017, 09:30 PM

Well, for these new planets their orbital periods are as short as a couple of days, so if tidally locked their "rotation" periods relative to the distant stars would be not much slower than that of the earth. I don't see that the magnetic fields would care if it's orbital or spin angular momentum.

Posted by: ngunn Feb 26 2017, 10:13 PM

I also wondered the same thing, and noted that all these worlds probably rotate a lot faster than Mercury and Venus. If it's about tidal locking per se then there is the counterexample of Ganymede which manages to have a magnetic field despite being tidally locked to Jupiter. Ganymede is a lot smaller than the Trappist-1 planets so if it can do it maybe they can.

Posted by: JRehling Feb 26 2017, 10:23 PM

I can only say "Suppose that tidal locking means no magnetic field…"

We really have very few examples and what conditions allow for a magnetic field are unknown at present. Particularly if we put that in terms of the properties that can be observed from light years away.

The fact that neither Venus nor Mars have appreciable magnetic fields is troubling. The fact that Mercury has one is intriguing. It remains a possibility that a lot of otherwise potentially hospitable exoplanets will have lost their H2O to stellar winds, but we can't say if that will be 5% or 95%, or what factors will determine it.

We may be able to resolve this question remotely – conceivably, we can see aurora around exoplanets, and atmospheric composition may give us other clues. This isn't something we can do at present, but we may know a lot about this in the decades to come.

Posted by: Explorer1 Feb 27 2017, 05:17 AM

If 59 day rotation is fast enough to get a magnetic field (albeit a weak one that certainly couldn't protect Mercury's primordial atmosphere), all of these Trappist-1 planets would easily spin fast enough to retain one. They are all much more massive than Mars too. Just so many variables, and so far out of reach of our magnetometers.

Posted by: Mongo Feb 28 2017, 08:21 PM

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.

Posted by: Explorer1 Mar 1 2017, 12:17 AM

Very cool; reminds me of J1407 ( ).

Posted by: marsbug Mar 8 2017, 02:47 AM

Somehow I'd mised that - a ring system with the mass of Earth, and 0.6 A.U. radius. Incredible!

Posted by: TheAnt Mar 19 2017, 01:29 PM

Of minor importance perhaps, yet more observations have revealed that Trappist 1h orbit the central star each 18.764 days, a value near what what predicted.
The radius turned out to be 0.715, while the calculated temperature at 169 K would make it a very cold world, which again is in line with predictions.

And a Youtube film where 'Universe sandbox' is used, even though it's probably not a fully reliable model.

Posted by: Mongo Apr 3 2017, 01:25 AM

The recent discovery of seven potentially habitable Earth-size planets around the ultra-cool star TRAPPIST-1 has further fueled the hunt for extraterrestrial life. Current methods focus on closely monitoring the host star to look for biomarkers in the transmission signature of exoplanet's atmosphere. However, the outcome of these methods remain uncertain and difficult to disentangle with abiotic alternatives. Recent exoplanet direct imaging observations by THIRSTY, an ultra-high contrast coronagraph located in La Trappe (France), lead us to propose a universal and unambiguous habitability criterion which we directly demonstrate for the TRAPPIST-1 system. Within this new framework, we find that TRAPPIST-1g possesses the first unambiguously habitable environment in our galaxy, with a liquid water percentage that could be as large as ∼ 90 %. Our calculations hinge on a new set of biomarkers, CO2 and CxH2(x+1)O (liquid and gaseous), that could cover up to ∼ 10 % of the planetary surface and atmosphere. THIRSTY and TRAPPIST recent observations accompanied by our new, unbiased habitability criterion may quench our thirst for the search for extraterrestrial life. However, the search for intelligence must continue within and beyond our Solar System.

Please note what day it is! tongue.gif

Posted by: JRehling Apr 3 2017, 01:51 AM

QUOTE (Mongo @ Apr 2 2017, 06:25 PM) *
Please note what day it is! tongue.gif

Also note that one of the authors is named Keg-Beer and the instrument is named THIRSTY, the star is named TRAPPIST (i.e., beer brewing monks), the title includes "brewing" and the chemical formula includes alcohol.

They've discovered extraterrestrial beer.

Posted by: Ron Hobbs Apr 3 2017, 02:50 AM

And did you notice this was published in the "Journal of Astrobrewology"?

"However, the search for intelligence must continue within and beyond our Solar System."


Posted by: JRehling Apr 13 2017, 05:47 AM

After that April Fools joke… here's an actual result about a Super Earth atmosphere. This is an exciting result, not only for the case of this one planet, and the general case of Super Earth atmospheres, but for the development of the technique:

I'd point out that the minimal radius seen in any of the filters is not necessarily the surface – it could be the level of cloud tops, in which case, we're learning about the composition of the atmosphere above the cloud tops.

I think a successful application of this technique is a nudge in the direction of favoring red dwarf systems over sunlike star systems in the contest for funding / further research. Of course, both merit interest, but this technique is unlikely to work for many planets in the habitable zone of nearby sunlike stars.

Posted by: tanjent Apr 13 2017, 02:55 PM

" it’s roughly Earth-sized, and has slightly less gravity than Earth (given its mass of about 1.6 times Earth’s, it has a surface gravity about 0.8 of ours)"

I'm no physicist, Phil, but isn't there a typo here somewhere? It would seem to make more sense if it had Earth's mass, and a diameter 1.6 times Earth's.

Posted by: scalbers Apr 13 2017, 04:26 PM

I wonder what the limits of this technique are with more narrowband filters and/or high resolution spectroscopy?

Posted by: JRehling Apr 14 2017, 02:09 AM

Surface gravity = m/r^2 (units in terms of Earth).

If m=1.6 and r=1.4, then g indeed is 0.8 of Earth's (1.6 / 1.4•1.4). The escape velocity, which is more relevant, would be about 0.9 of Earth's.

However, the errors in the measurements probably swamp the relevance of exact determinations of these things, and if we're concerned with the ability to hold an atmosphere, other, currently unmeasurable, factors would also be important.

Posted by: JRehling Apr 14 2017, 02:36 AM

Steve, I think the potential for this technique to be applied to produce finer understanding of transiting exoplanets' spectroscopic properties indicates certain possibilities for improvement, but they are limited. One of the limitations will be noise from the star. If the star dims a bit due to its own variability, we can't distinguish that from the effects of the planet's atmosphere. We can partially make up for this by making more observations, but improving SNR with more observations only goes so far. Interestingly, this problem can't be fixed with a bigger, better light bucket.

I could dive back into the Kepler data with which I was more familiar a few years ago, but the Catch-22 here seems to be that red dwarfs provide the vast majority of transiting HZ exoplanets, but they are generally more variable than sunlike stars. On the other hand, planets in the HZ of a red dwarf have a short orbital period so we can increase the number of observations more quickly.

I don't see why, in principle, we can't achieve arbitrarily good measurements of an exoplanet's spectrum with a very large number of observations. Looking down the road, we might want to build farms of multiple light buckets scanning exoplanets all the time.

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