TRAPPIST-1h: Drawing on K2 Data

by Paul Gilster on March 14, 2017

The data recently made available from Campaign 12 of K2 (the Kepler spacecraft’s two-reaction wheel mission) is already paying off in the form of information about the outermost planet in the TRAPPIST-1 system. Campaign 12 (described in Kepler Data on TRAPPIST-1 Coming Online) began on December 15 of 2016 and ran until March 4 of this year, though the spacecraft was in safe mode for a time, producing a 5-day data loss.

An international team including lead author Rodrigo Luger (University of Washington) and TRAPPIST-1 planet discoverer Michaël Gillon (Université de Liège) used the K2 data to constrain the period of TRAPPIST-1h, the outermost planet in this seven-planet system, which had only been observed to transit once before now. The team was also looking for additional planets (none were found) and, of course, examining resonances with the inner worlds.

The result: The orbital period of TRAPPIST-1h is found to be 18.764 days, a figure that fits into the pattern of resonance that the team’s theoretical work had predicted. TRAPPIST-1h is thus “…the seventh member of a complex chain, with three-body resonances linking every member.” The paper goes on to tell us that the planet has a radius of 0.715 R, and an equilibrium temperature of 169 K, meaning it orbits at the snow line.

Screenshot from 2017-03-14 11-40-01

Image: Figure 3 from Luger et al. Caption: The short cadence data folded on the four transits of planet h after correcting for TTVs and subtracting a simultaneous transit of b and a near-simultaneous flare. Other transits of b − g have not been removed and are visible in parts of the data. The data downbinned by a factor of 30 is shown as the orange line, and a transit model based solely on the Spitzer parameters is shown in red. The residuals (data minus this model) are shown at the bottom. Credit: Luger et al.

The paper notes that the stellar flux TRAPPIST-1h receives from its star is below what would be required to sustain liquid water under an atmosphere dominated by nitrogen, carbon dioxide and water (a hydrogen dominated atmosphere could theoretically make it possible). Nor is it on an orbit eccentric enough for tidal heating to warm the surface sufficiently. Nonetheless, tidal interactions play an important role in the evolution of the TRAPPIST-1 planets’ orbits. On the matter of formation and evolution, this was interesting:

The resonant structure of the system suggests that orbital migration may have played a role in its formation. Embedded in gaseous planet-forming disks, planets growing above ∼ 1 MMars create density perturbations that torque the planets’ orbits and trigger radial migration. One model for the origin of low-mass planets found very close to their stars proposes that Mars- to Earth-sized planetary embryos form far from their stars and migrate inward. The inner edge of the disk provides a migration barrier such that planets pile up into chains of mean motion resonances.

We can even extrapolate something about the speed of formation which, in turn, would have affected the compactness of the resulting system:

The TRAPPIST-1 system may thus represent a pristine surviving chain of mean motion resonances. Given that TRAPPIST-1’s planet-forming disk was likely low in mass and the planets themselves are low-mass, their migration was likely relatively slow. This may explain why TRAPPIST-1’s resonant chain is modestly less compact than chains in systems with more massive planets, which may have protected it from instability.


Image: An artist’s illustration of the seven TRAPPIST-1 planets. Sizes and relative positions are to scale. Credit: NASA/JPL-Caltech.

On the star TRAPPIST-1 itself, the researchers discovered it to be prone to star spots, making it possible to determine a rotational period of about 3.3 days, roughly comparable to nearby late M-dwarfs. The paper suggests an age in the range of 3 to 8 billion years. And note this re flare activity:

The presence of star spots and infrequent weak optical flares (0.38 d−1) for peak fluxes above 1% of the continuum, 30 times less frequent than active M6-M9 dwarfs are consistent with a low-activity M8 star, also arguing in favor of a relatively old system.

I notice that an energetic flare occurred at the end of the K2 campaign, and the authors promise that a full model of flare activity will be offered in an upcoming paper. This is useful information as we investigate questions of habitability among the inner worlds, for flares can damage atmospheres and have other adverse consequences for life.

It’s fascinating to consider how work like this develops from a damaged spacecraft. The paper points out that because of its two failed reaction wheels, the Kepler spacecraft’s rolling motion (created by imbalances in torque) induces strong instrumental effects, which lead to an increase of between 3 and 5 times in photometric noise compared to the original mission. The paper explains how removing these instrumental effects is done, but I continue to marvel at the fact that Kepler is still producing good science despite its serious internal problems.

The paper is Luger et al., “A terrestrial-sized exoplanet at the snow line of TRAPPIST-1,” submitted to Nature Astronomy (preprint).


{ 45 comments… read them below or add one }

tesh March 14, 2017 at 12:12

I wonder if there are any hints of moons in these data – though light curves themselves or through TTVs?


FrankH March 14, 2017 at 16:17

Most of these planets have reasonable Hill spheres (Drew calculated the value for one pair); a moon would have to be within the planet’s Hill sphere to exist.

Unfortunately, these planets have strong orbital resonances between each other. Moons would have to deal with strong periodic forces (basically, tides) from the other planets that would probably knock them out of orbit.

A hydrogen atmosphere around these planets is not feasible – Earth sized bodies in the temperature ranges postulated would quickly lose all their free hydrogen.


Michael Fidler March 15, 2017 at 0:10

Ah, but what about rings? Frankh that is a good point, look at Jupiter and Saturn, none of the moons in the solar system have their own moons.
You know we have discovered plasma, solids and gases in space but no liquids
so how difficult would it be to have a liquid planet or moon, with a collision between a mostly water world could a water planet form if is in the habitable zone?


Sanford Zane Meschkow March 14, 2017 at 12:29

One wonders what some methane plus a little hydrogen might do to boost the temperature a bit and lift it enough to make liquid water possible. Methane breathers?


Michael March 14, 2017 at 14:38

Methane and other hydrocarbons are powerful greenhouse gases, much more than hydrogen. I think this world is massive enough to hold onto a dense atmosphere similar to Earth’s. I suspect it is water/ice world with rocky outcrops on the starward side.


Ashley Baldwin March 15, 2017 at 16:18

I think you’re right. Going to be a good 18 months or so till there is enough TTV data for the simulations to really pin down the masses with precision but my guess is that “h” will top out at between three and five times Mars , though with a lot more volatiles .


Michael Fidler March 15, 2017 at 9:50

Early Earth had a hazy, methane-filled atmosphere.

“It has been proposed that enhanced methane fluxes to Earth’s early atmosphere could have altered atmospheric chemistry, initiating a hydrocarbon-rich haze reminiscent of Saturn’s moon Titan. The occurrence, cause, and significance of haze development, however, remain unknown. Here, we test and refine the “haze hypothesis” by combining an ultra-high-resolution sulfur- and carbon-isotope dataset with photochemical simulations to reveal the structure and timing of haze development. These data suggest that haze persisted for ∼1 million years, requiring a sustained biological driver. We propose that enhanced atmospheric CH4, implied by the presence of haze, could have had a significant impact on the escape of hydrogen from the atmosphere, effectively contributing to the terminal oxidation of Earth’s surficial environments ∼2.4 billion years ago.”


Andrew LePage March 14, 2017 at 13:11

It’s nice to see such a quick result for the orbit of TRAPPIST-1h just a few days after the K2 data became available. And with an 18.764 orbital period, the effective stellar flux would only be ~0.15 that of Earth – well beyond the outer edge of the conservatively defined HZ where the effective stellar flux would be 0.22 as described in my recent “Habitable Planet Reality Check” on this system:

And while the recent paper by Ramirez & Kaltenegger suggests that TRAPPIST-1h might be habitable if it has hydrogen in its atmosphere, I am dubious about the prospects of a sub-Earth size planet with maybe a third of the mass of the Earth that is 3 to 8 billion years old still releasing sufficient quantities free hydrogen and/or retaining it to maintain habitable conditions. Hopefully Hubble observations or, failing that, JWST may be able to detect the necessary hydrogen but I am doubtful.


torque_xtr March 14, 2017 at 13:25

The age of several GYr’s old means that steady luminosity already has been already reached. And that all inner worlds are scorched to ashes in the first hundred MYr’s when the primary’s luminosity was tens of times higher…


Ashley Baldwin March 14, 2017 at 15:55

The Kepler mission manager reckons it has enough fuel to last till summer 2018. The comments here on the mechanical faults seem to suggest that the great telescope is running on borrowed time. TESS is currently due for launch next March via Falcon 9 provided it has no further misfortunes . Summer launch at latest . It would be nice if there was to be a seemless mission handover with Kepler .

With just 69 days of active observation it was lucky to capture three transits though , which is a real break and helped with such an accurate constraint of period. I understand the transit timing variation method for determining planetary mass requires considerable computing power so it won’t be for a while that we see the improved figures and not until after more Spitzer observation later this year and likely next before we see the most precise results. Down to 10 % ultimately , but < 20 before the end of May.


andy March 14, 2017 at 16:18

There seem to be a lot of exoplanet results coming out these days! On the subject of compact, multi-planet systems, there’s a recent arXiv paper about the system of planets around Kepler-444A, including mass determinations for planets d and e (wide error bars, though iron planet compositions seem to be ruled out at the 95% level).

Mills & Fabrycky “Mass, Density, and Formation Constraints in the Compact, Sub-Earth Kepler-444 System including Two Mars-Mass Planets


Harry R Ray March 15, 2017 at 9:31

Now that the age(and PRESUMABLY the main sequence star vs Brown Dwarf)question has APPARENTLY been put to rest, we must now address why the star APPEARED TO BE so young due to its X ray(vs UV)discrepancy. One possible answer is that very recently(astronomically speaking) a planet ORIGINALLY orbiting INSIDE of TRAPPIST-1b spiraled ever-so-slowly toward, and finally beyond the Roache Lobe of the parent star, but; rather than being TOTALLY ENGULFED IMMEDIATELY, it was torn apart, forming an accretion disk. The disk material, over a period of millions of years, spiraled down onto the surface of the star, increasing its X-ray emission. If so, this temporary spike would be FAR LESS DAMAGING to the atmospheres of the planets than sustained emission at that level for billions of years.


Harry R Ray March 15, 2017 at 11:07

Buried deep within the paper(and thus NOT noticed much) was this: “…all of the planets except f and h have a tidal heat flux greater than Earth’s total heat flux…” What does THAT mean?


Henry Rouhivuori March 15, 2017 at 13:40

Perhaps not total 239 W/m2… but the internal heat flux ~0.09 W/m2. If so that means some of the Trappist-planets have molten cores, magnetic fields and active geology. I think.


Ashley Baldwin March 15, 2017 at 15:03

I noticed that too. It’s interesting that this system has been compared to the Galilean moons and the effects of their orbital resonance . Essentially additional energy will be pumped into these close planets via gravity , all on top of any conventional stellar energy flux . Europa and Io in particular already illustrate the outcome of tidal heating and this has been used to model the potential impact on the atmopheres of erstwhile exogas giant moons in the habitable zones of other stars . Essentially each giant would have its own additional local habitable zone dependent on tidal heating which could initiate runaway greenhouse on a sufficiently close large moon , rendering it dessicated and uninhabitable within a few millions of years . The effected area would depend on the mass of the gas giant . With other models suggesting that larger giants could spawn larger moons approaching or perhaps surpassing Mars mass. ( approaching the planetary masses for TRAPPIST-1 ) this issue becomes all the more important to the habitability of such moons . Clearly some gravitational / tidal energy might be beneficial if it allows moon cores to remain molten over billions of years potentially offering a protective magnetosphere and secondary atmosphere producing tectonics lubicated via any mantle volatile content .The same situation would seem to apply here only on a larger scale. Rene Heller has modelled this for exomoons extensively and it will be interesting to see if he picks up on this finding and explores the potential impact on TRAPPIST-1 and other likely related systems discovered by SPECULOOS .

Galilean moons apart and with no exomoons known as yet to explore the concept for real , TRAPPIST-1 may represent the first opportunity to do so. The parallel is striking . Heller has published most of his work in arXiv and it makes for for good reading , especially now that it has wider context and the chance of direct observational data through JWST . Pinning down the transit ephemerides of these planets between now and when JWST is fully operational in early 2019 ( and eventually the ELTs) is going to be critical for getting the best out of any transit spectroscopy .


Michael Fidler March 15, 2017 at 18:16

Rene Heller stacking up effect would also be good for finding rings around these planets. This is very similar to the lucky imaging used in amateur planetary imaging, could something like AutoStakkert! 2 be used to stack the light curves from these transits?
Then after stacking could a program similar to RegiStax 6 be used to improve the detail in the light curves?

“The ‘stacking up’ effect of these transit observations over time as the moon and planet transit the star in different configurations allows the detection. Because we need plentiful statistical data to make all this work, red dwarf stars are ideal candidates because habitable zone planets there have extremely short years and thus make many transits. According to Heller, moons down to Ganymede size should be detectable around M-dwarfs, while around warmer orange dwarf stars, exomoons about ten times Ganymede’s mass would be within range. G-class stars like the Sun are not represented well enough in the Kepler data because they lack sufficient transits.”


Harry R Ray March 16, 2017 at 9:24

Equally important is the precession and libration cycles. It could mean that in just a few tens of thousands of years,all planets except d and g would have a tidal heat flux higher than Earth’s total heat flux, then except c and e, and so on.


Harry R Ray March 15, 2017 at 13:31

Sorry, I meant “…higher…”, NOT “…greater…”, although I assume that the meaning is exactly the same(correct me if I’m wrong).


kzb March 16, 2017 at 8:30

The tidal heat flux comment is just a throw away line, but it deserves more explanation. It definitely says the tidal heat flux exceeds the total heat flux of Earth.

I wonder if this means the tidal heat flux used to be so high before the orbits were circularised?


ljk March 16, 2017 at 17:18

Using Sol as a gravitational lens to view exoplanets in detail – but we will need a space telescope 550 AU from our star:

To quote:

An Italian space scientist, Claudio Maccone, who chairs the International Academy of Astronautics Permanent SETI Committee, proposed that gravitational lensing could be used for something even more extraordinary: searching for radio signals from alien civilizations, using the sun as a gravitational lens to make an extraordinarily sensitive radio telescope.

Maccone did not invent the idea, which he calls focal, but he has studied it more deeply than anyone else. A radio telescope at a gravitational focal point of the sun would be incredibly sensitive. (Unlike an optical lens, a gravitational lens actually has many focal points that lie along a straight line, called a focal line; imagine a line running through an observer, the center of the lens, and the target.) For one particular frequency that has been proposed as a channel for interstellar communication, a telescope would amplify the signal by a factor of 1.3 quadrillion.


Harry R Ray March 17, 2017 at 9:35

BREAKING NEWS: Gliese 273 has two very interesting newly discovered planets! Gliese is a M3.5 star about 2-3 times as luminous as Proxima Centauri. Gliese 273b has a minimum mass of 2.79Me, and, depending on albedo, COULD have the same temperature as Earth. Gliese 273c has a minimum mass of 1.18Me with a 4.7234 day orbital period, with a temperature similar to TRAPPIST-1b(these two planets could be virtual clones of each other if Gliese 273b transits). If Gliese 273b DOES transit, either Hubble or Spitzer MUST BE USED for a 20 day CONTINUOUS observation session to see if Gliese 273b)orbital period: 18.6 days)TRANSITS AS WELL! If its radius COULD be determined, it should either prove or disprove Kipping and Chen’s 2Me MAXIMUM mass before transition to a sub-Neptune.


Michael Fidler March 17, 2017 at 22:10

Luyten’s Star has a Habitable Zone Planet
“GJ 273 (Gliese-Jahreiss star catalogue, number 273) is aka Luyten’s Star, an M3.5 dwarf some 12.2 light-years away.”
“So the Habitable Zone Super-Earth would have higher gravity than Earth with a similar composition. The radius would be ~1.33 Earth-radii, thus the surface gravity would be 1.63 gee”
What type of animals would form in the higher G force. Giants like the dinosaurs or dwarfs? I would expect that any intelligent life would be dwarfs maybe on 4 legs on these high gravity super earths or maybe something that slithers or insects types. Now with the infrared wavelengths of light from the red dwarf , they would need large eyes. So whats 3 foot tall, big head and big eyes and comes out of spacecrafts???
” With a distance of 3.8 parsec only, GJ 273 is the second nearest known planetary system – after Proxima Centauri – with a planet orbiting the circumstellar habitable zone.” (3.8 parsec = 12.2 lights years)
Luyten’s Star ( GJ 273) is only 1.2 light years from Procyon AB.


hiro March 18, 2017 at 17:04

Creatures living in water environment are less affected by gravity, I think or guess.


Michael Fidler March 18, 2017 at 23:05

Hiro, yes, you are right there, there have been many giants in our oceans, even some the most alien of all, the octopus. One area that could could have many alien life forms are the giant planets, Jupiter, Saturn, Uranus and Neptune. I remember my father saying that yeast could take over the planet earth, if it had enough to eat. So what about a environment full of amino acids, on earth the plants take the chemicals from the soil to make amino acids via photosynthesis. This is then used by other life forms for food, but what about an environment like the giant planets where amino acids could form naturally from lightning, internal planetary heat or evens just chemical reactions? In the gas and liquid of these planets or similar exoplanets you would have the perfect laboratory for mixing all the amino acids so imagine what giants might be eating them! So are we just the slime growing on the surface of a large asteroid and all the real life is growing in giant planets! Take a look at a picture of Earth next to Jupiter and see how huge a laboratory nature has in them to form life.


Harry R Ray March 19, 2017 at 14:24

I hope all of us readers grasp the irony of this, specifically, how the announcement was made. If this discovery was made JUST ONE YEAR AGO TODAY, it would have been done with great fanfare, probably an embargoed paper in Nature. Instead, due to Proxima b last August and TRAPPIST-1 last month, it is just a sidebar in a paper put up on ArXiv. A planet discovery has to be A REAL DOOZIE to get any kind of recognition anymore these days.


ljk March 19, 2017 at 16:12

Then it is the space community’s job to get these discoveries better recognition, both the professionals and interested amateurs. Such things are easier to do these days with social media.

Tabby’s Star was almost dismissed until it was pushed and promoted into the public spotlight.


Harry R Ray March 20, 2017 at 19:24

Be careful what you ask for, you may get it, ON STEROIDS! Case in point; The Kepler 452b announcement bummer. And I’m noteven going to comment ANY MORE about the Russian “ET signal” announcement, which garnered more comments on THIS website than ANY OTHER TOPIC BY FAR!!!


ljk March 21, 2017 at 13:24

You mean Kepler-Tabby’s Star discoveries like this:

The Russian SETI fiasco should be a strong lesson for all future SETI efforts and detections, but it probably won’t be until the various SETI/METI projects and the professional astronomical community start doing a better job at coordinating efforts. We have networks for reporting supernovae, so why not SETI? Is there still a stigma regarding aliens even in 2017? Time to grow up if that is the case.

As you may recall from this article I wrote last August, there are still some followups regarding that Russian SETI signal that I at least have yet to hear anything on:

If it was a terrestrial satellite or some other mistake, fine, but it needs to be reported, otherwise the usual nonsense about these things will have yet another log on the fire, if it is not too late already. Searching for alien intelligences should be one of the biggest, grandest things humanity can and should be doing. Yes Breakthrough Initiatives gave an infusion of cash, but that isn’t going to last forever, then what?


Harry R Ray March 22, 2017 at 9:31

No. ALL of the Boyajian-esque type stars are M dwarfs and(to ME, anyway) have VIABLE natural explanations. However, if Jason Wright does ANOTHER interview in “Atlantic”………..


Andrew LePage March 21, 2017 at 13:30

In case anyone is interested, I have posted a “Habitable Planet Reality Check” on GJ 273 or Luyten’s Star:

Bottom line is that GJ 273b looks to be a fairly good candidate for being a potentially habitable exoplanet. It probably is not quite as good as Kepler 186f or Kepler 452b or (in some regards) Proxima Centauri b, but it would easily make a “Top Ten” list of potentially habitable planets deserving of a closer look.


Harry R Ray March 17, 2017 at 9:36

Sorry, I meant “If Gliese 273c DOES transit…”


Michael Fidler March 19, 2017 at 11:09

Exponential Distance Relation and Near Resonances in the Trappist-1 Planetary System.
“We report in this paper a new exponential relation distance of planets in the newly discovered exoplanetary system of the Trappist-1 star, and we comment on near orbital mean motion resonances among the seven planets. We predict that possible smaller planets could be found inside the orbit of the innermost discovered Planet b.”


Michael Fidler March 19, 2017 at 22:41

Assessing the Habitability of the TRAPPIST-1 System Using a 3D Climate Model
Eric T. Wolf
“The TRAPPIST-1 system provides an extraordinary opportunity to study multiple terrestrial extrasolar planets and their atmospheres. Here we use the National Center for Atmospheric Research Community Atmosphere Model version 4 to study the possible climate and habitability of the planets in the TRAPPIST-1 system. We assume ocean-covered worlds, with atmospheres comprised of N2, CO2, and H2O, and with orbital and geophysical properties defined from observation. Model results indicate that the inner three planets (b, c, and d) presently reside interior to the inner edge of the traditional liquid water habitable zone. Thus if water ever existed on the inner planets, they would have undergone a runaway greenhouse and lost their water to space, leaving them dry today. Conversely the outer 3 planets (f, g, and h) fall beyond the maximum CO2 greenhouse outer edge of the habitable zone. Model results indicate that the outer planets cannot be warmed despite as much as 30 bar CO2 atmospheres, instead entering a snowball state. The middle planet (e) represents the best chance for a presently habitable ocean-covered world in the TRAPPIST-1 system. Planet e can maintain at least some habitable surface area with 0 – 2 bar CO2, depending on the background N2 content. Near present day Earth surface temperatures can be maintained for an ocean-covered planet e with either 1 bar N2 and 0.4 bar CO2, or a 1.3 bar pure CO2 atmosphere.”

So it looks like TRAPPIST-1e is it, according to this article.


Harry R Ray March 20, 2017 at 10:56

They do NOT take the recent tidal heat flux data into account, probably because their paper had already been submitted BEFORE that data came out. Combining the two papers, I now see TRAPPIST-1g as the best bet, though only time will tell. ArXive posts UPDATED VERSIONS of original papers when original authors take NEW DATA into account. I expect to see an updated version of THIS paper with the tidal heat flux data INCLUDED. LOOK FOR IT!


Harry R Ray March 22, 2017 at 9:40

MORE BREAKING NEWS: Kepler 1649b has been CONFIRMED as a roughly 1Re planet orbiting a M5V star with 1.5-2 times the luminosity of Proxima Centauri in an orbit very similar to Proxima b. The Incident flux level(IFL)is similar to Venus’s, however; if it is a water world with a PERMANENT CLOUD COVER at the stellar point, it could be potentially habitable(NOT LIKELY THOUGH, because it falls on the EXACT INNER EDGE of the OPTIMISTIC habitable zone, which may or may NOT prompt Abel Mendez to add it to his HEC Catalog).


Michael Fidler March 23, 2017 at 3:26

Hit paywall on this one, any other ID? Just how close is this system?


Harry R Ray March 23, 2017 at 9:41

I did it the OLD-FASHIONED way: I googled Kepler 1649b. Then I hit “Kepler- 1649b: An Exo-Venus in the Solar Neighborhood-IOPscience. The article with the same title(by Isabel Angelo, Jason F Rowe, Steve B. Howell, Elisa V. Quintana, Martin Still, Andrew W. Mann, Ben Burningham, Thomas Barclay, David R. Ciardi, Daniel Huber)popped up. Then I hit paywall(sort of). Only the abstract was available on THE ASTRONOMICAL JOURNAL. To access the PDF, you must either have an acceptable individual login, an acceptable institutional login, OR; you have to BUY the article! I hope that YOU can do BETTER! GOOD LUCK!


Harry R Ray March 23, 2017 at 10:32

I went to the “rumor-mill” website and got SOME specifics. HERE THEY ARE: Orbital period 8.68909 days(vs Proxima b’s 11.186 day orbital period). Star’s effective temperature 3240+/-61K(vs Proxima Centauri’s Teff of 3042+/- 117K). Stellar Mass 0.219+/-0.039Msun. Stellar radius 0.252+/- 0.039Rsun. Planet radius 1.08 +/- 0.15 Rearth. Planet orbital semi-major axis 0.0514+/-0.0028 AU. Incedent Flux Level(IFL) 2.30+/- 0.65(!?) IFLearth. LOWER END WOULD MAKE IT MORE HABITABLE THAN Kepler 438b!!!


Harry R Ray March 22, 2017 at 10:12

EVEN MORE BREAKING NEWS!!!!! Brian Cox is confident, that if Planet 9 DOES EXIST, it will be discovered NEXT WEEK! For details, log on to


Michael Fidler March 22, 2017 at 23:31

Formation of TRAPPIST-1 and other compact systems.
Chris Ormel, Beibei Liu, Djoeke Schoonenberg
(Submitted on 20 Mar 2017)
“TRAPPIST-1 is a nearby 0.08 Msun M-star, which has recently been found to harbor a planetary system of at least 7 Earth-mass planets, all within 0.1 au. The configuration confounds theorists as the planets are not easily explained by either in situ or migration models. In this Letter we present a complete scenario for the formation and orbital architecture of the TRAPPIST-1 system. In our model, planet formation starts at the H2O iceline, where pebble-size particles — whose origin is the outer disk — concentrate to trigger streaming instabilities. After their formation, protoplanets quickly mature by pebble accretion. Planet growth stalls at Earth mass, where the planet’s gravitational feedback on the disk keeps pebbles at bay. The planets are transported by Type I migration to the inner disk, where they stall at the magnetospheric cavity and end up in mean motion resonances. During disk dispersal, the cavity radius expands and the inner-most planets escape resonance. We argue that the model outlined here can also be applied to other compact systems and that the many close-in super-Earth systems are a scaled-up version of TRAPPIST-1. We also hypothesize that few close-in compact systems harbor giant planets at large distances, since they would have stopped the pebble flux from the outer disk.”
This is a fascinating bit of sleuthing and bodes well for planets similar to earth in the habitable zone of the huge number of red dwarfs that have these miniature solar systems. Jupiter is an example of this in that an active moon (Io) is the closet to the planet and the next moon (Europa) is a water world with the next two outer moons ( Ganymede and Callisto) having large sub surface oceans.


Michael Fidler March 23, 2017 at 12:42

Formation of TRAPPIST-1 and other compact systems.
Here’s the article.


Harry R Ray March 24, 2017 at 9:35

An UNIMPEACHABLE(i.e. ABSOLUTELY NO DOUBT)Brown Dwarf has been discovered with the mass of NINETY JUPITERS! That translates to a mass of 0.09423Msun(the only reason I mention this HERE is that TRAPPIST-1 has a mass of ONLY 0.08Msun!)! The reaso for this is this is the first “pristine” Brown Dwarf with a composition of 99.95%Hydrogen and Helium. For details, go to


Michael Fidler March 26, 2017 at 2:36

Some interesting art work from Guillem H. Pongiluppi via ArtStation on Trappist1 planetary system.


Michael Fidler March 26, 2017 at 9:54

Doing some fun calculating, but wonder if the figures are correct. Taking the size of the Red Dwarf Trappist 1 and up scaling it to our Sun size gives a 9 times enlargement. When you multiply the orbit of Trappist 1h (0.063 AU) by 9 it ends up being 0.567 AU, which is just outside Mercury furthest distance from the Sun 0.466 AU. This seems to be a very miniature system so would some other scaling factor work better such as mass, which would be around 12 times enlargement. It does not seem to scale well even with are inner solar system, Mercury to Mars. Could it be that we are dealing with a completely different aspect of geology and planet structures – possible even chemical makeup such as carbon planets!


ljk March 29, 2017 at 14:53


Inventing Tools for Detecting Life Elsewhere

Caltech astronomers develop new strategy for future telescopes

Recently, astronomers announced the discovery that a star called TRAPPIST-1 is orbited by seven Earth-size planets. Three of the planets reside in the “habitable zone,” the region around a star where liquid water is most likely to exist on the surface of a rocky planet. Other potentially habitable worlds have also been discovered in recent years, leaving many people wondering: How do we find out if these planets actually host life?

At Caltech, in the Exoplanet Technology Laboratory, or ET Lab, of Associate Professor of Astronomy Dimitri Mawet, researchers have been busy developing a new strategy for scanning exoplanets for biosignatures—signs of life such as oxygen molecules and methane. These chemicals—which don’t naturally stick around for long because they bind with other chemicals—are abundant on Earth largely thanks to the living creatures that expel them. Finding both of these chemicals around another planet would be a strong indicator of the presence of life.

In two new papers to be published in The Astrophysical Journal and The Astronomical Journal, Mawet’s team demonstrates how this new technique, called high-dispersion coronagraphy, could be used to look for extraterrestrial biosignatures with the planned Thirty Meter Telescope (TMT), which, when completed by the late 2020s, will be the world’s largest optical telescope.

Using theoretical and laboratory models, the researchers show that this technique could detect biosignatures on Earth-like planets around M-dwarf stars, which are smaller and cooler than our sun and the most common type of star in the galaxy. The strategy could also be used on stars like our own sun, using future space telescopes such as NASA’s proposed Habitable Exoplanet Imaging Mission (HabEx) and Large UV/Optical/IR Surveyor (LUVOIR).

“We’ve shown this technique works in theory and in the lab, so our next step is to show it works on the sky,” says Ji Wang, one of the lead authors on the two new papers and a postdoctoral scholar in the Mawet lab. The team will test the instrumentation on the W. M. Keck Observatory in Hawaii this year or next.

Full article here:


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