I provide the link with the official announcement: https://www.nasa.gov/press-release/nasa-to-host-news-conference-on-discovery-beyond-our-solar-system
The recently detected TRAPPIST-1 planetary system represents a unique opportunity to extend the nascent field of comparative exoplanetology into the realm of temperate terrestrial worlds. It is composed of at least three Earth-sized planets similar in sizes and irradiations to Earth and Venus transiting an ultra-cool dwarf star only 39 light-years away. Thanks to the Jupiter-size and infrared brightness of their host star, the planets are amenable for detailed atmospheric characterization with JWST, including for biosignatures detection. Our Spitzer Exploration Science Program aims to prepare and optimize the detailed study of this fascinating planetary system through the two following complementary sub-programs: (1) a 480 hrs continuous monitoring of the star to explore its full inner system up to its ice line in a search for any other transiting object(s) (planet, moon, Trojan) with a sensitivity high enough to detect any body as small as Ganymede, and (2) the observation of ~130 transits of the planets (520 hrs). This second part has two goals. First, to measure precisely the planets' masses and eccentricities through the Transit Timing Variations method, to constrain strongly their compositions and energy budgets. Secondly, to measure with an extremely high precision the planets' effective radii at 4.5 microns to assess, when combined with future HST/WFC3 observations, the presence of an atmosphere around them. The two complementary parts of this program will make it a long-lasting legacy of Spitzer to the fields of comparative exoplanetology and astrobiology, by providing the necessary measurements on the inner system of TRAPPIST-1 (complete census, masses, eccentricities, first insights on atmospheres) required to initiate and optimize the detailed atmospheric characterization of its different components with JWST and other future facilities.
Hmm, it's a real press conference with all those people present and not just a telecon, so I agree that it looks to be something at least 'majorish'. It's probably also something the interests general public, because otherwise they wouldn't bother with the AMA. My guess is something nice about TRAPPIST-1 planets' atmospheres, although it's not to me clear how much they could see with warm Spitzer (only NIR photometry and no spectroscopy available). Exoplanets is not my field, though.
ABSTRACTOwing to over 1500 hours of monitoring including a recent 20-d long follow-up with the Spitzer Space Telescope, we have now constrained the architecture of TRAPPIST-1's system up to its ice line. There is no doubt left regarding the system uniqueness for Earth-sized comparative planetology and for the search for extrasolar habitats. The present request for DDT will fulfill the urgent need to inform the community about TRAPPIST-1 planets in order to guide their follow-up, notably in the context of the upcoming JWST Cycle 1 proposal. We request 23 HST/WFC3 orbits to assess the presence of extended atmospheres.OBSERVING DESCRIPTIONWe propose to observe the transits of TRAPPIST-1's planets with WFC3 on Dec.4, Dec. 29, and Jan. 10 to obtain their tansmission spectra and assess the presence of extended atmospheres.
ABSTRACTWe have recently completed reconnaissance studies of the TRAPPIST-1 system with the Spitzer and Hubble Space Telescopes. Owing to a 20-d long follow-up with Spitzer, we have now constrained the system architecture up to the ice line. Thanks to 4 non-consecutive HST/STIS orbits, we have determined the potential for further studies of the system in the UV--notably to search for hydrogen exospheres--and characterized the UV environment of TRAPPIST-1's planets, which is an essential contributing factor to their potential habitability. These reconnaissance studies with the synergetic Great Observatories emphasize the system uniqueness for Earth-sized comparative planetology and for the search for extrasolar habitats.We request here 5 consecutive HST/STIS orbits to build upon our UV exploratory program and confirm the presence of an extended exosphere exosphere around TRAPPIST-1~c. These observations will inform us on its volatile reservoir while complementing the insights gained with HST/WFC3 (GOs 14500 and 14873). Our request for immediate HST/STIS followup will fulfill the urgent need to inform the community about TRAPPIST-1 planets in order to guide their follow-up, notably in the context of the upcoming JWST Cycle 1 proposal.OBSERVING DESCRIPTIONWe propose to observe the transits of TRAPPIST-1's planets with WFC3 on Dec.4, Dec. 29, and Jan. 10 to obtain their tansmission spectra and assess the presence of extended atmospheres.
I agree it most likely is regarding detection of atmospheres.
“With more data, we could perhaps detect methane or see water features in the atmospheres, which would give us estimates of the depth of the atmospheres,” said Hannah Wakeford, the paper’s second author, at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.Observations from future telescopes, including NASA’s James Webb Space Telescope, will help determine the full composition of these atmospheres and hunt for potential biosignatures, such as carbon dioxide and ozone, in addition to water vapor and methane. Webb also will analyze a planet’s temperature and surface pressure – key factors in assessing its habitability.
Is there still observing time up for grabs on JWST in its initial observing campaigns or has this already been allocated?
Quote from: Star One on 02/20/2017 11:36 pmIs there still observing time up for grabs on JWST in its initial observing campaigns or has this already been allocated?Director's Discretionary Early Release Science deadline has not passed yet.
I doubt it is that big, for a start Hubble likely doesn't have the sensitivity to make that sort of detection. This is the last Nasa press release regarding Hubble looking for atmospheres on the Trappist planets;https://www.nasa.gov/press-release/nasa-s-hubble-telescope-makes-first-atmospheric-study-of-earth-sized-exoplanetsQuote“With more data, we could perhaps detect methane or see water features in the atmospheres, which would give us estimates of the depth of the atmospheres,” said Hannah Wakeford, the paper’s second author, at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.Observations from future telescopes, including NASA’s James Webb Space Telescope, will help determine the full composition of these atmospheres and hunt for potential biosignatures, such as carbon dioxide and ozone, in addition to water vapor and methane. Webb also will analyze a planet’s temperature and surface pressure – key factors in assessing its habitability.
Quote from: as58 on 02/21/2017 08:23 amQuote from: Star One on 02/20/2017 11:36 pmIs there still observing time up for grabs on JWST in its initial observing campaigns or has this already been allocated?Director's Discretionary Early Release Science deadline has not passed yet.Could this amongst other things be a way of strengthening an application for time on it?
I'm thinking it's transmission spectrum detection of some constituent of atmosphere of some/one of TRAPPIST-1 planet(s). I don't think that has been done with ~Earth-sized planets before.
Shooting blindly into the dark, maybe they have some indication of near-me planets in Earth-type orbits around K- or G-class stars in the immediate galactic neighbourhood from the detailed radial velocity measurements that they've been taking recently. I know that Epsilon Eridani is considered a good candidate.
It is about TRAPPIST-1, definitely.This is from the famous Didier Queloz, who has worked with Gillon;https://www.twitter.com/DidierQueloz/status/833976887500234754https://www.twitter.com/DidierQueloz/status/834027647046918145It will probably be an announcement 1c is likely a waterworld.
#NASA will announce that TRAPPIST-1 has 7 Earth-sized planets - 6 within/close to star's habitable zone #astrobiology #extrasolar #astronomy
That looks to me pure speculation, and I'm not convinced;http://nasawatch.com/archives/2017/02/spitzer-discove.htmlIt is not impossible there are other bodies, indeed earlier proposals remarked on other potential transit features not related to the already identified planets. But if they had found other objects I suspect they would have been mentioned in the most recent proposals, even if obliquely.I also don't see why representatives of both Spitzer and Hubble would need to be there.
Quote from: Alpha_Centauri on 02/21/2017 04:17 pmThat looks to me pure speculation, and I'm not convinced;http://nasawatch.com/archives/2017/02/spitzer-discove.htmlIt is not impossible there are other bodies, indeed earlier proposals remarked on other potential transit features not related to the already identified planets. But if they had found other objects I suspect they would have been mentioned in the most recent proposals, even if obliquely.I also don't see why representatives of both Spitzer and Hubble would need to be there.Also "just" finding more planets doesn't feel to me quite exciting enough for the press conference.
Am I right in thinking that the HST is insufficiently sensitive to detect free oxygen in the atmosphere and they will have to wait for JWST to come on line to do this?
That looks to me pure speculation, and I'm not convinced;
Quote from: Alpha_Centauri on 02/21/2017 04:17 pmThat looks to me pure speculation, and I'm not convinced;I'm not at all convinced. From reading his "source" documents I think he has got confused over HST orbit planning ... and as as58 says, it really doesn't account for the panel composition or the excitement (heck, I've found a 7 planet system; well, helped to :-) )--- Tony
It's not impossible that they'll also announce more planets in the system as well. If it was 7 I think that would make it the most heavily populated exo planet solar system.
Quote from: Star One on 02/21/2017 05:57 pmIt's not impossible that they'll also announce more planets in the system as well. If it was 7 I think that would make it the most heavily populated exo planet solar system.True ... however Kepler-90 (KOI-351) has 7 and HD 10180 has at least 7 and possibly nine, so while unusual, I doubt it would warrant the amount of excitement we're seeing.--- Tony
Quote from: Star One on 02/21/2017 05:57 pmIt's not impossible that they'll also announce more planets in the system as well. If it was 7 I think that would make it the most heavily populated exo planet solar system.True ... however Kepler-90 (KOI-351) has 7 and HD 10180 has at least 7 and possibly nine, so while unusual, I doubt it would warrant the amount of excitement we're seeing.Edit: also, if there are additional *transiting* planets, I'd expect them to wait for the K2 campaign 12 release ...--- Tony
I think the excitement - if the rumors are true - would come from the suggestion that 6 of these 7 Earth-sized worlds are in the habitable zone. That would indeed be very interesting, as we could probe how increasing irradiation by the star affects their atmospheres, making that star something of a "Rosetta stone" for Earth-size-exoplanet atmosphere studies.
Apparently it is true (I think someone has got their embargo dates wrong);http://uk.businessinsider.com/earth-size-worlds-seven-trappist-1-2017-2?r=US&IR=T
Why all the atmosphere experts then? Feels like there should be more to this announcement.
It is possible that most of the planets confirmed thus circling far TRAPPIST-1 could be in the star's habitable zone. The inner 6 planets are probably rocky in composition and may be just the right temperature for liquid water to exist (between 0 - 100 degrees C) - if they have any water, that is. The outermost 7th planet still needs some more observations to nail down its orbit and composition.
I appreciate the excitement in scientific circles but, as I understand it, TRAPPIST-1 only barely classifies above a Brown Dwarf. That makes for very tight orbits to make for a thermal 'goldilocks zone'.The problem I've always had with these dim red dwarf 'habitable zone' planets is that all the other physical characteristics are likely to make them sterile, most notably being tidally locked, really close to the photosphere (and thus likely to be bathed in lethal X- and UV-radiation levels) and probably without atmosphere due to lack of magnetic field )due to said tidal locking) and close proximity to the primary. They make for useful studies and doubtless have their own unique charms (Pluto has taught us that there is no such thing as an 'uninteresting planetary body'). I guess I just have difficulty hyping these bodies up in my mind.In my mind, with current sensing capabilities, the optimum habitable target world we're likely to find would be a hypothetical Galilean Moon-sized object orbiting a detected 'Warm Jupiter' in the habitable zone of a K- to A-class primary.
Anyway, b and f look interesting; they would appear possibly volatile-rich given the densities. b in particular could be steamy.
Quote from: Alpha_Centauri on 02/22/2017 12:31 pmAnyway, b and f look interesting; they would appear possibly volatile-rich given the densities. b in particular could be steamy.I doubt "b" ... given the resonances, I expect it's Io-like due to tidal heating. On the plus side, this means those nearer the ice line may be warmer than just flux would suggest, though I haven't run any numbers.On planets around M dwarfs in general, like Ben, I'm sceptical due to both locking and desiccation when the stars are young.--- Tony
Is that all we're going to do be downbeat about this, no wonder those in society who devalue science are having so much success these days.
The exoplanets around TRAPPIST-1 are almost all very nearly the same mass or slightly more massive than the Earth, so we should expect they would be likely to have an atmosphere.
Quote from: Alpha_Centauri on 02/22/2017 12:31 pmAnyway, b and f look interesting; they would appear possibly volatile-rich given the densities. b in particular could be steamy.I doubt "b" ... given the resonances, I expect it's Io-like due to tidal heating. On the plus side, this means those nearer the ice line may be warmer than just flux would suggest, though I haven't run any numbers.
Quote from: Star One on 02/22/2017 01:24 pmIs that all we're going to do be downbeat about this, no wonder those in society who devalue science are having so much success these days.Why do you think this is downbeat? I'm sceptical over the habitability of planets around M dwarfs. That doesn't make them uninteresting or even mean there aren't plenty of habitable planets around other types of star.It also doesn't mean I'm ruling it out, just that there are good reasons to doubt that just because a planet is in the HZ means it is at all close to being Earth-like or habitable. Much depends on system formation, and most models don't allow enough volatiles for atmosphere / water to survive the initial flare activity.--- Tony
Did I imagine it or did I read that they had spent 1500h observing this system using the HST.
Quote from: Star One on 02/22/2017 03:25 pmDid I imagine it or did I read that they had spent 1500h observing this system using the HST.I missed the article when it was up, but there's no way they could've gotten anywhere close to that number of hours.edit: I think 1500 hours refers to total time with all telescopes including Spitzer, on which they did get several hundred hours. A quick look at accepted proposals shows about 40 orbits of HST observations.
edit: I think 1500 hours refers to total time with all telescopes including Spitzer, on which they did get several hundred hours. A quick look at accepted proposals shows about 40 orbits of HST observations.
Owing to over 1500 hours of monitoring including a recent 20-d long follow-up with the Spitzer Space Telescope, we have now constrained the architecture of TRAPPIST-1's system up to its ice line
Other researchers are already using the Hubble Space Telescope to hunt for atmospheres on the TRAPPIST-1 planets. Kepler is also observing the system and will gather data that can better pin down the planetary masses, says Courtney Dressing, an astronomer at the California Institute of Technology in Pasadena. And the TRAPPIST team is building four new 1-metre-diameter telescopes in Chile to continue the work.“For all the worlds that we see in science fiction, these are even more extraordinary,” says Hannah Wakeford, an exoplanet scientist at Goddard.
The Hubble Space Telescope characterized the atmospheres of TRAPPIST-1B and TRAPPIST-1C, finding that the two worlds probably aren't encircled by hydrogen and helium rich atmospheres, meaning their atmospheres could resemble our own. Researchers will be able to get an even better look at these worlds in the future.NASA's James Webb Space Telescope (JWST) — Hubble's telescope successor expected to launch in 2018 — should be able to peer deeply into the atmospheres of alien planets to try to see if they really could be like our own.
I've read in a few articles now that the fifth planet is considered the most habitable, why is this?
The TRAPPIST-1 system contains a total of seven planets, all around the size of Earth. Three of them -- TRAPPIST-1e, f and g -- dwell in their star's so-called "habitable zone."ť The habitable zone, or Goldilocks zone, is a band around every star (shown here in green) where astronomers have calculated that temperatures are just right -- not too hot, not too cold -- for liquid water to pool on the surface of an Earth-like world.While TRAPPIST-1b, c and d are too close to be in the system's likely habitable zone, and TRAPPIST-1h is too far away, the planets' discoverers say more optimistic scenarios could allow any or all of the planets to harbor liquid water. In particular, the strikingly small orbits of these worlds make it likely that most, if not all of them, perpetually show the same face to their star, the way our moon always shows the same face to the Earth. This would result in an extreme range of temperatures from the day to night sides, allowing for situations not factored into the traditional habitable zone definition. The illustrations shown for the various planets depict a range of possible scenarios of what they could look like.
Those brown, green, and blue zones in that TRAPPIST-1 system image seem to be IMO oddly placed. If we're looking just at irradiation and comparing to the Solar System, d should be easily inside the green zone, g well outside in the blue and f just about on the edge of green and blue. Or is there some more detail going into defining those zones (e.g. different stellar spectrum)?.
Yes, I think the runaway greenhouse limit for the smallest red dwarfs is around 0.9 S_Earth. So if scaled properly, the HZ is slightly further out for a smaller star. The paper preprint linked above says that they did climate models on all of them, and b, c, d ran into the runaway greenhouse state, while e, f, g remained temperate (h is likely too cold). EDIT: if we are looking for a name for the system, I think we should call it ...
Andrew LePage February 22, 2017 at 15:02> In particular, let’s see what Andrew LePage comes up with in his own Habitable Zone Reality Check.Well, I’ve got a lot of data to digest before a write a “Habitable Planet Reality Check” (hopefully to come out in the next few days), but at first blush there does indeed seem to be reason to believe that at least one of these worlds is “potentially habitable”… maybe more. And the fact that TRAPPIST-1e has a fairly well determined radius and mass with a resulting density suggestive of a volatile-rich planet means that Earth-size planets orbiting small red dwarfs *CAN* hold onto their water and atmospheres despite flare activity, excessive X-ray/XUV flux, etc.. That’s a hopeful sign about the potential habitability of exoplanets like Proxima Centauri b or even Kepler 186f, among many others.
Lords of Kobol! Could it be the Great Colonies?
Arxiv preprint on UV / XUV and habitability in the Trappist-1 system. Long story short, if there is an Earth-like moderately dense atmosphere with an ozone layer - all good. That failing, not even UV-resistant bacteria can make it.https://arxiv.org/abs/1702.06936
EDIT: if we are looking for a name for the system, I think we should call it ...
Quote from: Bynaus on 02/22/2017 07:35 pmEDIT: if we are looking for a name for the system, I think we should call it ... [In the spirit of the suggestion. ]Presumably you mean a name for the star? (TRAPPIST-1 is a catalog designation.) The system would then be called 'the [name of star] system'!The IAU Working Group on Star Names might go for Axanar. The only two catalog designations I can find are 2MASS J23062928-0502285 and the later TRAPPIST-1 suggesting the star was discovered in the Two Micron All-Sky Survey of 1997-2001. So, there's unlikely to be any of the traditional or historical names for which the WGSN has a preference. The WGSN might object though if they consider a name from the title of a fan-made Star Trek movie to be a name of a principally commercial nature. Also, the film concerns the 'Battle of Axanar' and the WGSN also prohibit names related to military activities!
XRays won't penetrate far into the water - as long as you've got water oceans, you can have underwater life. Of course if you have that, then you probably have an atmosphere above it.
The system is only about 500 Ma old, so biogenic O2-rich atmospheres/ozone layers seem not very likely anyway.
That number is only a very rough minimum. The age of extremely long lived M dwarfs is notoriously hard to pin down because they evolve so slowly. The star could be billions of years old, especially because it seems to be a quiet star flare-wise.
Quote from: the_roche_lobe on 02/23/2017 08:13 amThat number is only a very rough minimum. The age of extremely long lived M dwarfs is notoriously hard to pin down because they evolve so slowly. The star could be billions of years old, especially because it seems to be a quiet star flare-wise.On the other hand, it has a high metallicity ([Fe/H] = +0.04), which suggests it can be *too* old. Similarly, it has a fast rotation rate. But as you say, 0.5 billion is a minimum. It could easily be a few billion.
Yes, I think the runaway greenhouse limit for the smallest red dwarfs is around 0.9 S_Earth. So if scaled properly, the HZ is slightly further out for a smaller star. The paper preprint linked above says that they did climate models on all of them, and b, c, d ran into the runaway greenhouse state, while e, f, g remained temperate (h is likely too cold).
I was thinking to myself that this solar system model may be giving us a glimpse of what planetary systems look like in the absence of a gas giant that cleans smaller rocky bodies out of the inner orbital space.
Greg Laughlin is always worth reading. Here’s the relevant paragraph from his post today:“2MASS J20362926-0502285, now much better known as TRAPPIST-1, straddles the boundary between the lowest mass main sequence stars and the highest mass brown dwarfs. Depending on precisely what its mass and metallicity turn out to be, it could either be arriving at self-sustaining core hydrogen fusion, which would make it a main sequence star (about a 60% chance) or it could be currently achieving its peak brown dwarf luminosity and bracing for a near-eternity of cooling into obscurity (about a 40% chance).”Also quite interesting here is his take on the future of this system, assuming TRAPPIST-1 is indeed a main sequence star:“An object with solar composition and 0.08 solar masses never turns into a red giant. As time goes on, it maintains a near-constant radius, and slowly burns nearly all of its hydrogen into helium. In roughly 10 trillion years, TRAPPIST-1 will reach a maximum temperature of ~4000K, pushing it briefly toward K-dwarf status for a few tens of billions of years, before eventually running out of fuel and fading out as a degenerate helium dwarf.”
An interesting thought has occurred to me. ...
Quote from: JasonAW3 on 02/23/2017 06:24 pmAn interesting thought has occurred to me. ...That's not quite how it works. The star is, by far, the dominant tidal influence on the planet's rotation states.Test your idea though: The mass ratio of TRAPPIST-1 to its planets is about the same as that of Jupiter to its moons, Saturn to its moons, and Uranus to its moons, with rather similar levels of compactness (Jupiter being somewhat less of course). What are the rotation states are the moons of Jupiter, Saturn, and Uranus?(Also, I suspect the torque on a planet's rotation by a passing planet would probably average to zero, given circular orbits)
By the way there's a special Google Doodle today celebrating this discovery.IAU really need to give this star a proper name.
[W]ater vapor in the upper atmosphere could photo-dissociate and sustain an outflow of escaping hydrogen. The stellar Ly-α line is bright enough to perform transit spectroscopy, and we detect marginal flux decreases in localized, high-velocity ranges during the transit of planet b, and shortly after thetransit of planet c. This could hint at the presence of extended hydrogen exospheres around the two inner planets, and suggest that atmospheric escape might play an active role in the evolution of all TRAPPIST-1 planets.
What impact could larger planets such as gas and ice giants further out in the system have on the habitability of these rocky worlds?
The discovery paper (supplement) discusses the long-term stability of the system and it is mentioned that it's very hard to keep even the known system stable.
Quote from: as58 on 02/24/2017 04:49 pmThe discovery paper (supplement) discusses the long-term stability of the system and it is mentioned that it's very hard to keep even the known system stable.Isn't that true even for our solar system? I recall reading the accuracy of our orbital predication degrades past a couple hundred million years.
Quote from: gosnold on 02/24/2017 05:39 pmQuote from: as58 on 02/24/2017 04:49 pmThe discovery paper (supplement) discusses the long-term stability of the system and it is mentioned that it's very hard to keep even the known system stable.Isn't that true even for our solar system? I recall reading the accuracy of our orbital predication degrades past a couple hundred million years.Sure, to some extent. But in case of TRAPPIST-1 most simulations apparently lead to disruption of the system on a time scale of a million years or less.
Judy Schmidt @SpaceGeckI've got an accurate little TRAPPIST-1 system set up in Blender. This is 1 year of looking at the star from planet e.
Meanwhile, we can do at least one experiment: Examine this system for radio signals that would indicate the presence of intelligence. And indeed, the SETI Institute used its Allen Telescope Array last year to observe the environs of Trappist 1, scanning through ten billion radio channels in search of signals. No transmissions were detected, although new observations are in the offing. How sensitive was this search? Assuming that the putative inhabitants of this solar system can use a transmitting antenna as large as the 500 meter FAST radio telescope in China to beam their messages our way, then the Allen Array could have found a signal if the aliens use a transmitter with 100 kilowatts of power or more. This is only about ten times as energetic as the radar down at your local airport. And whether or not Trappist 1 has inhabitants, its discovery has underlined the growing conviction that the universe is replete with real estate on which biology could both arise and flourish. If you still think the rest of the universe is sterile, you are surely singular, and probably wrong.
When the news about the seven planets of TRAPPIST-1 broke, I immediately wondered what Andrew LePage’s take on habitability would be. A physicist and writer with numerous online essays and a host of articles in magazines like Scientific American and Sky & Telescope, LePage is also a specialist in the processing and analysis of remote sensing data. He has put this background in data analytics to frequent use in his highly regarded ‘habitable planet reality checks,’ which can be found on his Drew ex Machina site. Having run a thorough analysis of the TRAPPIST-1 situation the other day, Drew now gives us the gist of his findings, which move at least several of the TRAPPIST-1 planets into a potentially interesting category indeed.
Public tries to name 7 new planets after Nasa discovery- with chaotic resultshttp://www.telegraph.co.uk/news/2017/03/02/nasa-asks-public-help-name-7-new-plants-chaotic-results/
Quote from: Star One on 03/03/2017 04:33 pmPublic tries to name 7 new planets after Nasa discovery- with chaotic resultshttp://www.telegraph.co.uk/news/2017/03/02/nasa-asks-public-help-name-7-new-plants-chaotic-results/One of the reasons the IAU was founded was to stop this kind of chaos when it comes to the naming of celestial bodies (the arguments over the naming of Neptune were quite vicious). But in order to prevent other people giving exoplanets names, the IAU has to get round to naming them itself! I know Eric Mamajek, who is a member of the Executive Committee Working Group on the Public Naming of Planets and Planetary Satellites, is keen that the IAU runs another round of its successful NameExoWorlds process, though apparently there's opposition (professional astronomers can get a bit snobby at times IMO).
That's class-M dwarves for you: Once they hit main sequence, there's really no way to easily tell the difference between 100 million or 10 billion years old!
Quote from: Ben the Space Brit on 03/13/2017 03:39 pmThat's class-M dwarves for you: Once they hit main sequence, there's really no way to easily tell the difference between 100 million or 10 billion years old!From my limited understanding of that article it's the radiation output that's proving contradictory ageing wise.
Quote from: Star One on 03/13/2017 03:53 pmQuote from: Ben the Space Brit on 03/13/2017 03:39 pmThat's class-M dwarves for you: Once they hit main sequence, there's really no way to easily tell the difference between 100 million or 10 billion years old!From my limited understanding of that article it's the radiation output that's proving contradictory ageing wise.It's worse than that. I think that article references the 1.4 day stellar rotation period from Nature. But the actual rotation period is more like 3.3 days.So that is contradictory as well, indicating a much older star (>= ~1bn). However, gyrochronology is poorly constrained for M dwarfs.--- Tony
Don't stars slow down as that get older or does that only apply to ones like our Sun?
If I understand correctly, the problem is that the different indicators are giving different age ranges for TRAPPIST-1. This would indicate either the existing theoretical models are wrong or (and this is probably more likely) TRAPPIST-1 is an anomalous body and we can't take anything about it for granted based on analysis of other M8s.
Quote from: Ben the Space Brit on 03/13/2017 04:39 pmIf I understand correctly, the problem is that the different indicators are giving different age ranges for TRAPPIST-1. This would indicate either the existing theoretical models are wrong or (and this is probably more likely) TRAPPIST-1 is an anomalous body and we can't take anything about it for granted based on analysis of other M8s.Could it be because it's just on the line to being a brown dwarf.
Perhaps and I don't know if this is a possibility that it started off as a brown dwarf but somehow crossed the boundary into being a red dwarf at a later point?
Quote from: Star One on 03/13/2017 04:46 pmQuote from: Ben the Space Brit on 03/13/2017 04:39 pmIf I understand correctly, the problem is that the different indicators are giving different age ranges for TRAPPIST-1. This would indicate either the existing theoretical models are wrong or (and this is probably more likely) TRAPPIST-1 is an anomalous body and we can't take anything about it for granted based on analysis of other M8s.Could it be because it's just on the line to being a brown dwarf.My understanding is that although astronomers think it is a very low-mass star rather than a brown dwarf, this is by no means certain and it could actually be a brown dwarf. It's very difficult to distinguish between a very low-mass star and a young brown dwarf.QuotePerhaps and I don't know if this is a possibility that it started off as a brown dwarf but somehow crossed the boundary into being a red dwarf at a later point?It would've had to have absorbed sufficient additional mass at some point after formation - preferably hydrogen, but most kinds of mass would do (how much mass would depend on how close the brown dwarf was to being a red dwarf!). One possibility is that a hot Jupiter spiraled in too close and crashed into the brown dwarf, the current exoplanets forming after this event.
The TRAPPIST-1 system is the first transiting planet system found orbiting an ultra-cool dwarf star. At least seven planets similar to Earth in radius and in mass were previously found to transit this host star. Subsequently, TRAPPIST-1 was observed as part of the K2 mission and, with these new data, we report the measurement of an 18.764 d orbital period for the outermost planet, TRAPPIST-1h, which was unconstrained until now. This value matches our theoretical expectations based on Laplace relations and places TRAPPIST-1h as the seventh member of a complex chain, with three-body resonances linking every member. We find that TRAPPIST-1h has a radius of 0.715 Earth radii and an equilibrium temperature of 169 K, placing it at the snow line. We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.
We have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.
Quote from: Star One on 03/14/2017 08:36 amWe have also measured the rotational period of the star at 3.3 d and detected a number of flares consistent with an active, middle-aged, late M dwarf.So how old is an active, middle-aged, late M dwarf?
While the long spin-down times of ultra-cool dwarfs prevent derivation of a robust gyrochronology relation, the rotationalperiod of TRAPPIST-1 is roughly in the middle of the period distribution of nearby late M dwarfs, suggesting an age in the range3−8 Gyr based on a star formation history that declines slightly with time.
... suggesting an age in the range 3−8 Gyr based on a star formation history that declines slightly with time.
Quote from: as58 on 03/14/2017 05:01 pm... suggesting an age in the range 3−8 Gyr based on a star formation history that declines slightly with time.Assuming Gyr means Gigayear, or 1 billion years, then the Trappist star is 3-8 billion years old, which is the same "range" as Sol, which is 4.55 billion years old. Do I have that right?
Now, Lingam and Loeb have calculated that exact probability. Comparing the TRAPPIST-1 planets to Earth and Mars, they found that the travel time between one planet and the next is shorter by a factor of a hundred. This boosts the chance that life can survive such a harrowing journey. They also found that the likelihood of one planet’s debris landing on another is larger by a factor of 20 or so.Altogether, the possibility that life can play hopscotch from one planet to the next is a few thousand times higher among the TRAPPIST-1 worlds than the possibility that it did the same from Mars to Earth.
I sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.
Quote from: Star One on 03/14/2017 08:50 pmI sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.It's a good question: there are several searches looking for "solar twins" ... from memory, we've found a few candidates but not many.But Trappist-1 is not one of them ... its relative velocity is too high for it to be a close neighbour for long. Again from memory, its velocity puts it on the YD/OD boundary.--- Tony
Quote from: jebbo on 03/27/2017 03:26 pmQuote from: Star One on 03/14/2017 08:50 pmI sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.It's a good question: there are several searches looking for "solar twins" ... from memory, we've found a few candidates but not many.But Trappist-1 is not one of them ... its relative velocity is too high for it to be a close neighbour for long. Again from memory, its velocity puts it on the YD/OD boundary.--- TonyForgive my ignorance Tony but what is the YD/OD boundary?
Quote from: clongton on 03/27/2017 10:33 pmQuote from: jebbo on 03/27/2017 03:26 pmQuote from: Star One on 03/14/2017 08:50 pmI sometimes wonder how many of the stars in the locality came out of the same stellar nursery as our sun.It's a good question: there are several searches looking for "solar twins" ... from memory, we've found a few candidates but not many.But Trappist-1 is not one of them ... its relative velocity is too high for it to be a close neighbour for long. Again from memory, its velocity puts it on the YD/OD boundary.--- TonyForgive my ignorance Tony but what is the YD/OD boundary?I was wondering that as well TBH.
young disk/old disk? Though they're more commonly called thin and thick disks.
We analyze short cadence K2 light curve of the TRAPPIST-1 system. Fourier analysis of the data suggests Prot=3.295±0.003 days. The light curve shows several flares, of which we analyzed 42 events, these have integrated flare energies of 1.26×1030−1.24×1033 ergs. Approximately 12% of the flares were complex, multi-peaked eruptions. The flaring and the possible rotational modulation shows no obvious correlation. The flaring activity of TRAPPIST-1 probably continuously alters the atmospheres of the orbiting exoplanets, making these less favorable for hosting life.
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.
The newly detected TRAPPIST-1 system, with seven low-mass, roughly Earth-sized planets transiting a nearby ultra-cool dwarf, is one of the most important exoplanet discoveries to date. The short baseline of the available discovery observations, however, means that the planetary masses (obtained through measurement of transit timing variations of the planets of the system) are not yet well constrained. The masses reported in the discovery paper were derived using a combination of photometric timing measurements obtained from the ground and from the Spitzer spacecraft, and have uncertainties ranging from 30\% to nearly 100\%, with the mass of the outermost, P=18.8d, planet h remaining unmeasured. Here, we present an analysis that supplements the timing measurements of the discovery paper with 73.6 days of photometry obtained by the K2 Mission. Our analysis refines the orbital parameters for all of the planets in the system. We substantially improve the upper bounds on eccentricity for inner six planets (finding e<0.02 for inner six known members of the system), and we derive masses of 0.79±0.27M⊕, 1.63±0.63M⊕, 0.33±0.15M⊕, 0.24+0.56−0.24M⊕, 0.36±0.12M⊕, 0.566±0.038M⊕, and 0.086±0.084M⊕ for planets b, c, d, e, f, g, and h, respectively.
Figure 4 indicates that – to within the errors of our determinations – the four most distant planets are consistent with pure water compositions, and in any event, are substantially less dense either Mars or Venus.
There’s more than one way to appreciate the results. While Tamayo was working on his simulations, he was approached by Matt Russo, a fellow postdoc and jazz guitarist who thought the TRAPPIST-1 resonances looked familiar from music theory. Now, coordinated with the release of Tamayo’s paper, Russo, Tamayo and the musician Andrew Santaguida have teamed up to translate the system’s intricate arrangement of passing worlds into a musical composition.The seventh planet, h, orbits about once every three weeks. Sped up some 200 million times and expressed in sound waves, that frequency is a C note. From there, the known ratios between planets determine every other planet’s signature note. Together the notes form a major ninth chord. “It’s really remarkable that it worked out like that,” Russo said. “Even with a different pattern of resonances, you wouldn’t get a chord that sounds as good.”On top of that, the team added drumbeats for whenever an inner planet overtakes an outer neighbor — moments that correspond to close gravitational interactions among the planets. Compared to human percussion, Russo said, “It’s a super-creative drummer. It’s doing something that nobody else would think of.”
One of the primary surprises of exoplanet detections has been the discovery of compact planetary systems, whereby numerous planets reside within ~0.5 au of the host star. Many of these kinds of systems have been discovered in recent years, indicating that they are a fairly common orbital architecture. Of particular interest are those systems for which the host star is low mass, thus potentially enabling one or more of the planets to lie within the habitable zone of the host star. One of the contributors to the habitability of the Earth is the presence of a substantial moon whose tidal effects can stabilize axial tilt variations and increase the rate of tidal pool formation. Here, we explore the constraints on the presence of moons for planets in compact systems based on Hill radii and Roche limit considerations. We apply these constraints to the TRAPPIST-1 system and demonstrate that most of the planets are very likely to be worlds without moons.
With Nasa’s James Webb Space Telescope not due to launch until late 2018, the scientists turned to computer models to find out whether the Trappist-1 planets could have long-lived atmospheres. From details of the Trappist-1 system, which lies 39 light years distant, they worked out the intensity of the stellar wind – the rush of high energy particles streaming out of the star – and the effect it would have on the seven orbiting planets.
The intensity of the solar wind destroyed the atmospheres of the inner Trappist-1 planets within millions of years. But planets further out fared better, their atmospheres surviving for billions of years, the models found. According to the scientists, while the seventh planet around the star is considered too cold for liquid water to exist on the surface, the sixth planet, Trappist-1g, appears to be the most likely home for life in the Trappist-1 system.
Exoplanet Puzzle Cracked by Jazz MusiciansQuoteThere’s more than one way to appreciate the results. While Tamayo was working on his simulations, he was approached by Matt Russo, a fellow postdoc and jazz guitarist who thought the TRAPPIST-1 resonances looked familiar from music theory. Now, coordinated with the release of Tamayo’s paper, Russo, Tamayo and the musician Andrew Santaguida have teamed up to translate the system’s intricate arrangement of passing worlds into a musical composition.The seventh planet, h, orbits about once every three weeks. Sped up some 200 million times and expressed in sound waves, that frequency is a C note. From there, the known ratios between planets determine every other planet’s signature note. Together the notes form a major ninth chord. “It’s really remarkable that it worked out like that,” Russo said. “Even with a different pattern of resonances, you wouldn’t get a chord that sounds as good.”On top of that, the team added drumbeats for whenever an inner planet overtakes an outer neighbor — moments that correspond to close gravitational interactions among the planets. Compared to human percussion, Russo said, “It’s a super-creative drummer. It’s doing something that nobody else would think of.”https://www.quantamagazine.org/exoplanet-puzzle-cracked-by-jazz-musicians/
Why are you posting stuff by a nutjob with a penchant for caps as if it means anything?
Aug. 11, 2017TRAPPIST-1 is Older Than Our Solar SystemIf we want to know more about whether life could survive on a planet outside our solar system, it’s important to know the age of its star. Young stars have frequent releases of high-energy radiation called flares that can zap their planets' surfaces. If the planets are newly formed, their orbits may also be unstable. On the other hand, planets orbiting older stars have survived the spate of youthful flares, but have also been exposed to the ravages of stellar radiation for a longer period of time.Scientists now have a good estimate for the age of one of the most intriguing planetary systems discovered to date -- TRAPPIST-1, a system of seven Earth-size worlds orbiting an ultra-cool dwarf star about 40 light-years away. Researchers say in a new study that the TRAPPIST-1 star is quite old: between 5.4 and 9.8 billion years. This is up to twice as old as our own solar system, which formed some 4.5 billion years ago.The seven wonders of TRAPPIST-1 were revealed earlier this year in a NASA news conference, using a combination of results from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, NASA's Spitzer Space Telescope, and other ground-based telescopes. Three of the TRAPPIST-1 planets reside in the star’s "habitable zone," the orbital distance where a rocky planet with an atmosphere could have liquid water on its surface. All seven planets are likely tidally locked to their star, each with a perpetual dayside and nightside.At the time of its discovery, scientists believed the TRAPPIST-1 system had to be at least 500 million years old, since it takes stars of TRAPPIST-1’s low mass (roughly 8 percent that of the Sun) roughly that long to contract to its minimum size, just a bit larger than the planet Jupiter. However, even this lower age limit was uncertain; in theory, the star could be almost as old as the universe itself. Are the orbits of this compact system of planets stable? Might life have enough time to evolve on any of these worlds?"Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago," said Adam Burgasser, an astronomer at the University of California, San Diego, and the paper's first author. Burgasser teamed up with Eric Mamajek, deputy program scientist for NASA's Exoplanet Exploration Program based at NASA's Jet Propulsion Laboratory, Pasadena, California, to calculate TRAPPIST-1's age. Their results will be published in The Astrophysical Journal.It is unclear what this older age means for the planets' habitability. On the one hand, older stars flare less than younger stars, and Burgasser and Mamajek confirmed that TRAPPIST-1 is relatively quiet compared to other ultra-cool dwarf stars. On the other hand, since the planets are so close to the star, they have soaked up billions of years of high-energy radiation, which could have boiled off atmospheres and large amounts of water. In fact, the equivalent of an Earth ocean may have evaporated from each TRAPPIST-1 planet except for the two most distant from the host star: planets g and h. In our own solar system, Mars is an example of a planet that likely had liquid water on its surface in the past, but lost most of its water and atmosphere to the Sun’s high-energy radiation over billions of years.However, old age does not necessarily mean that a planet's atmosphere has been eroded. Given that the TRAPPIST-1 planets have lower densities than Earth, it is possible that large reservoirs of volatile molecules such as water could produce thick atmospheres that would shield the planetary surfaces from harmful radiation. A thick atmosphere could also help redistribute heat to the dark sides of these tidally locked planets, increasing habitable real estate. But this could also backfire in a "runaway greenhouse" process, in which the atmosphere becomes so thick the planet surface overheats – as on Venus."If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years," Burgasser said. Fortunately, low-mass stars like TRAPPIST-1 have temperatures and brightnesses that remain relatively constant over trillions of years, punctuated by occasional magnetic flaring events. The lifetimes of tiny stars like TRAPPIST-1 are predicted to be much, much longer than the 13.7 billion-year age of the universe (the Sun, by comparison, has an expected lifetime of about 10 billion years)."Stars much more massive than the Sun consume their fuel quickly, brightening over millions of years and exploding as supernovae," Mamajek said. "But TRAPPIST-1 is like a slow-burning candle that will shine for about 900 times longer than the current age of the universe."Some of the clues Burgasser and Mamajek used to measure the age of TRAPPIST-1 included how fast the star is moving in its orbit around the Milky Way (speedier stars tend to be older), its atmosphere’s chemical composition, and how many flares TRAPPIST-1 had during observational periods. These variables all pointed to a star that is substantially older than our Sun.Future observations with NASA's Hubble Space Telescope and upcoming James Webb Space Telescope may reveal whether these planets have atmospheres, and whether such atmospheres are like Earth's."These new results provide useful context for future observations of the TRAPPIST-1 planets, which could give us great insight into how planetary atmospheres form and evolve, and persist or not," said Tiffany Kataria, exoplanet scientist at JPL, who was not involved in the study.Future observations with Spitzer could help scientists sharpen their estimates of the TRAPPIST-1 planets’ densities, which would inform their understanding of their compositions.For more information about TRAPPIST-1, visit:https://exoplanets.nasa.gov/trappist1Elizabeth LandauJet Propulsion Laboratory, Pasadena, Calif.
This illustration shows what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right).Credits: NASA/JPL-Caltech
TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its seven planets orbit very close to it.Credits: NASA/JPL-Caltech
How on Earth have they managed that when a number of papers have said they will stripped of their atmospheres by their parent star.
Quote from: Star One on 09/01/2017 10:52 amHow on Earth have they managed that when a number of papers have said they will stripped of their atmospheres by their parent star.The history of astronomy and astrophysics is a history of seemingly-unequivocal paper calculations having to be thrown out of the window because the universe stubbornly refuses to adhere to them. In fairness, any theoretical modelling must necessarily be prone to huge uncertainties due to the difficulty in acquiring sufficient and reliable data to slot into your equations at a distance of nearly 40 l.y.The lesson? Never fall into the trap of announcing 'definitive' conclusions. Always add the contingency "given the best data currently to hand".
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could harbor liquid water on their surfaces. Ultraviolet observations are essential to measuring their high-energy irradiation and searching for photodissociated water escaping from their putative atmospheres. Our new observations of the TRAPPIST-1 Lyα line during the transit of TRAPPIST-1c show an evolution of the star emission over three months, preventing us from assessing the presence of an extended hydrogen exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape. However, TRAPPIST-1e to h might have lost less than three Earth oceans if hydrodynamic escape stopped once they entered the habitable zone (HZ). We caution that these estimates remain limited by the large uncertainty on the planet masses. They likely represent upper limits on the actual water loss because our assumptions maximize the X-rays to ultraviolet-driven escape, while photodissociation in the upper atmospheres should be the limiting process. Late-stage outgassing could also have contributed significant amounts of water for the outer, more massive planets after they entered the HZ. While our results suggest that the outer planets are the best candidates to search for water with the JWST, they also highlight the need for theoretical studies and complementary observations in all wavelength domains to determine the nature of the TRAPPIST-1 planets and their potential habitability.
Boss and colleagues studied the star with astrometric methods, which measure the position of a star in the sky with accuracy great enough to see the slight changes in motion caused by its planets. Astrometry is hard to do, but its rewards are potentially great, as it can provide accurate estimates of a planet’s mass, a value that challenges other planet detection methods. Unlike radial velocity techniques, astrometry works best at planets on long orbital periods, which makes it ideal for trying to locate gas giants like Jupiter in outer system orbits.The researchers used Carnegie’s CAPSCam astrometric camera, attached to the 2.5-meter du Pont telescope at Las Campanas Observatory (Chile) to determine the upper limits for gas giants at TRAPPIST-1. The result: There are no planets larger than 4.6 times Jupiter’s mass orbiting the star with a period of one year, and no planets larger than 1.6 times Jupiter’s mass orbiting the star with 5 year periods. Given how tightly packed the TRAPPIST-1 planets are, these are wide orbits, and as Boss says, “There is a lot of space for further investigation between the longer-period orbits we studied here and the very short orbits of the seven known TRAPPIST-1 planets.”
The recently detected TRAPPIST-1 planetary system, with its seven planets transiting a nearby ultracool dwarf star, offers the first opportunity to perform comparative exoplanetology of temperate Earth-sized worlds. To further advance our understanding of these planets' compositions, energy budgets, and dynamics, we are carrying out an intensive photometric monitoring campaign of their transits with the Spitzer Space Telescope. In this context, we present 60 new transits of the TRAPPIST-1 planets observed with Spitzer/IRAC in February and March 2017. We combine these observations with previously published Spitzer transit photometry and perform a global analysis of the resulting extensive dataset. This analysis refines the transit parameters and provides revised values for the planets' physical parameters, notably their radii, using updated properties for the star. As part of our study, we also measure precise transit timings that will be used in a companion paper to refine the planets' masses and compositions using the transit timing variations method. TRAPPIST-1 shows a very low level of low-frequency variability in the IRAC 4.5-μm band, with a photometric RMS of only 0.11% at a 123-s cadence. We do not detect any evidence of a (quasi-)periodic signal related to stellar rotation. We also analyze the transit light curves individually, to search for possible variations in the transit parameters of each planet due to stellar variability, and find that the Spitzer transits of the planets are mostly immune to the effects of stellar variations. These results are encouraging for forthcoming transmission spectroscopy observations of the TRAPPIST-1 planets with the James Webb Space Telescope.
Given TESS' eminent launch this March, a thought occurs to me: is Trappist-1 among the stars to be observed by TESS? Any way to follow this up?
That graph is from version 1, they corrected it. Below is from version 4.Also R* = ~0.12RsolRemember also that the Trappist planets have Rearth around 1 or less. They may observable be but it would be tight, relatively low S/N.
The seven Earth-size planets of TRAPPIST-1 are all mostly made of rock, with some having the potential to hold more water than Earth, according to a new study published in the journal Astronomy and Astrophysics. The planets' densities, now known much more precisely than before, suggest that some planets could have up to 5 percent of their mass in water -- which is 250 times more than the oceans on Earth.The form that water would take on TRAPPIST-1 planets would depend on the amount of heat they receive from their star, which is a mere 9 percent as massive as our Sun. Planets closest to the star are more likely to host water in the form of atmospheric vapor, while those farther away may have water frozen on their surfaces as ice. TRAPPIST-1e is the rockiest planet of them all, but still is believed to have the potential to host some liquid water."We now know more about TRAPPIST-1 than any other planetary system apart from our own," said Sean Carey, manager of the Spitzer Science Center at Caltech/IPAC in Pasadena, California, and co-author of the new study. "The improved densities in our study dramatically refine our understanding of the nature of these mysterious worlds."Since the extent of the system was revealed in February 2017, researchers have been working hard to better characterize these planets and collect more information about them. The new study offers better estimates than ever for the planets' densities.What is TRAPPIST-1?TRAPPIST-1 is named for the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, which discovered two of the seven planets we know of today -- announced in 2016. NASA's Spitzer Space Telescope, in collaboration with ground-based telescopes, confirmed these planets and uncovered the other five in the system.Since then, NASA's Kepler space telescope has also observed the TRAPPIST-1 system, and Spitzer began a program of 500 additional hours of TRAPPIST-1 observations, which will conclude in March. This new body of data helped study authors paint a clearer picture of the system than ever before -- although there is still much more to learn about TRAPPIST-1.The TRAPPIST-1 planets huddle so close to one another that a person standing on the surface of one of these worlds would have a spectacular view of the neighboring planets in the sky. Those planets would sometimes appear larger than the Moon looks to an observer on Earth. They may also be tidally locked, meaning the same side of the planet is always facing the star, with each side in perpetual day or night. Although the planets are all closer to their star than Mercury is to the Sun, TRAPPIST-1 is such a cool star, some of its planets could still, in theory, hold liquid water.In the new study, scientists led by Simon Grimm at the University of Bern in Switzerland created computer models to better simulate the planets based on all available information. For each planet, researchers had to come up with a model based on the newly measured masses, the orbital periods and a variety of other factors -- making it an extremely difficult, "35-dimensional problem," Grimm said. It took most of 2017 to invent new techniques and run simulations to characterize the planets' compositions.It is impossible to know exactly how each planet looks, because they are so far away. In our own solar system, the Moon and Mars have nearly the same density, yet their surfaces appear entirely different."Densities, while important clues to the planets' compositions, do not say anything about habitability. However, our study is an important step forward as we continue to explore whether these planets could support life," said Brice-Olivier Demory, co-author at the University of Bern.Based on available data, here are scientists' best guesses about the appearances of the planets:TRAPPIST-1b, the innermost planet, is likely to have a rocky core, surrounded by an atmosphere much thicker than Earth's. TRAPPIST-1c also likely has a rocky interior, but with a thinner atmosphere than planet b. TRAPPIST-1d is the lightest of the planets -- about 30 percent the mass of Earth. Scientists are uncertain whether it has a large atmosphere, an ocean or an ice layer -- all three of these would give the planet an "envelope" of volatile substances, which would make sense for a planet of its density.Scientists were surprised that TRAPPIST-1e is the only planet in the system slightly denser than Earth, suggesting it may have a denser iron core than our home planet. Like TRAPPIST-1c, it does not necessarily have a thick atmosphere, ocean or ice layer -- making these two planets distinct in the system. It is mysterious why TRAPPIST-1e has a much rockier composition than the rest of the planets. In terms of size, density and the amount of radiation it receives from its star, this is the most similar planet to Earth.TRAPPIST-1f, g and h are far enough from the host star that water could be frozen as ice across these surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules of Earth, such as carbon dioxide."It is interesting that the densest planets are not the ones that are the closest to the star, and that the colder planets cannot harbor thick atmospheres," said Caroline Dorn, study co-author based at the University of Zurich, Switzerland.How do we know?Scientists are able to calculate the densities of the planets because they happen to be lined up such that when they pass in front of their star, our Earth- and space-based telescopes can detect a dimming of its light. This is called a transit. The amount by which the starlight dims is related to the radius of the planet.To get the density, scientists take advantage of what are called "transit timing variations." If there were no other gravitational forces on a transiting planet, it would always cross in front of its host star in the same amount of time -- for example, Earth orbits the Sun every 365 days, which is how we define one year. But because the TRAPPIST-1 planets are packed so close together, they change the timing of each other's "years" ever so slightly. Those variations in orbital timing are used to estimate the planets' masses. Then, mass and radius are used to calculate density.Next StepsThe next step in exploring TRAPPIST-1 will be NASA's James Webb Space Telescope, which will be able to delve into the question of whether these planets have atmospheres and, if so, what those atmospheres are like. A recent study using NASA's Hubble Space Telescope found no detection of hydrogen-dominated atmospheres on planets TRAPPIST-1d, e and f -- another piece of evidence for rocky composition -- although the hydrogen-dominated atmosphere cannot be ruled out for g.Illustrations of these worlds will change as ongoing scientificinvestigations home in on their properties."Our conceptions of what these planets look like today may change dramatically over time," said Robert Hurt, senior visualization scientist at the Spitzer Science Center. "As we learn more about these planets, the pictures we make will evolve in response to our improved understanding.For more information about TRAPPIST-1, visit:https://exoplanets.nasa.gov/trappist1
Too much water helps planetary habitability not one bit. And while we find the availability of surface water a useful way of describing a potentially habitable world, we’re learning that some planets may have water in such abundance that life may never have the chance to emerge. It would be a shame if the numerous worlds orbiting TRAPPIST-1 fell into this scenario, but a multidisciplinary team from Arizona State University is making a strong case for the prospect.
The TRAPPIST-1 system provides an exquisite laboratory for understanding exoplanetary atmospheres and interiors. Their mutual gravitational interactions leads to transit timing variations, from which Grimm et al. (2018) recently measured the planetary masses with precisions ranging from 5% to 12%. Using these masses and the <5% radius measurements on each planet, we apply the method described in Suissa et al. (2018) to infer the minimum and maximum CRF (core radius fraction) of each planet. Further, we modify the maximum limit to account for the fact that a light volatile envelope is excluded for planets b through f. Only planet e is found to have a significant probability of having a non-zero minimum CRF, with a 0.7% false-alarm probability it has no core. Our method further allows us to measure the CRF of planet e to be greater than (49 +/- 7)% but less than (72 +/- 2)%, which is compatible with that of the Earth. TRAPPIST-1e therefore possess a large iron core similar to the Earth, in addition to being Earth-sized and located in the temperature zone.