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Seven Planets around TRAPPIST-1

The red dwarf known as TRAPPIST-1 could not have produced a more interesting scenario. Today we learn that the star, some 40 light years out in the constellation Aquarius, hosts seven planets, all of which turn out to be comparable to the Earth in terms of size. Moreover, these worlds were discovered through the transit method, meaning we have mass and radius information for all of them. Today’s report in Nature tells us that three of the planets lie in the habitable zone, and thus could have liquid water on their surfaces.


TRAPPIST-1 b, c, d, e, f, g and h are the worlds in question, and all but TRAPPIST-1h appear to be rocky in composition, based on density measurements drawn from the mass and radius information. Drawing on existing climate models, the innermost planets b, c and d are probably too hot to allow liquid water to exist, while h may be too distant and cold. But the European Southern Observatory is reporting that TRAPPIST-1e, f and g orbit within the star’s habitable zone, leaving us with the possibility of oceans and the potential for life.

Caution compels me to home in on the word ‘potential’ in the above sentence, and also to remind readers that we’ve seen many planets described as being in the habitable zone for which later study made a much less compelling case. Thus I appreciate lead author Michaël Gillon (STAR Institute, University of Liège), whose enthusiasm is evident when he says “This is an amazing planetary system — not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth!” But I also look forward to the close analysis the community gives habitable zone issues and what it will reveal. In particular, let’s see what Andrew LePage comes up with in his own Habitable Zone Reality Check.

My own reservation about habitability: The age of TRAPPIST-1, thought to be in the range of 500 million years, points to a young dwarf of the kind given to flare activity. Here I note a paper from Peter Wheatley (University of Warwick), with Michaël Gillon as one of the co-authors. In “Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1,” Wheatley and team present XMM-Newton X-ray observations of TRAPPIST-1, finding ‘a relatively strong and variable coronal X-ray source with an X-ray luminosity similar to that of the quiet Sun.” A snip from the paper:

The TRAPPIST-1 system presents a fabulous opportunity to study the atmospheres of Earth-sized planets as well as the complex and uncertain mechanisms controlling planet habitability. Whatever the mechanisms at play, it is clear that these planets are subject to X-ray and EUV irradiation that is many-times higher than experienced by the present-day Earth and that is sufficient to significantly alter their primary and any secondary atmospheres. The high energy fluxes presented here are vital inputs to atmospheric studies of the TRAPPIST-1 planets.

None of that is to downplay the significance of this discovery, but simply to put it in context (it also should remind us how many factors come into play in the word ‘habitability’). Even so, with seven planets in a compact system around this dim red star, we certainly have some interesting real estate to work with. And we’ll certainly have plenty to investigate in a system with multiple transits. TRAPPIST-1 has about 8 percent the mass of the Sun. To be in the habitable zone here, a planet needs to be close to the parent star — indeed, the planetary orbits around TRAPPIST-1 are not much larger than what we find among Jupiter’s larger moons, and much smaller than the orbit of Mercury in our own system.

That means that transits are deep, as the planets are close to a very small star. Gillon and co-author Amaury Triaud (University of Cambridge) worked with space and ground instruments to make this detection, which follows up their original discovery of three Earth-sized planets there, announced in 2016. The TRAPPIST-South telescope at La Silla produced data complemented by the Very Large Telescope (Paranal) and the Spitzer Space Telescope and several other ground based instruments in the course of these observations.

The news conference on the TRAPPIST-1 findings goes online just as I publish this, and I’m sure we’ll have more to say about this fascinating system in short order.


Comments on this entry are closed.

  • Robert G February 22, 2017, 14:26

    A topic related to this that I’ve never seen discussed is the stability of planetary orbits as the number of planets increases. Our solar system has four rocky inner worlds (excluding things like Ceres, Juno, Pallas etc.)

    If you were to set up a solar system simulation, how many small worlds could you possibly put in stable orbits close around the various star classes?

    Is seven the highest we’ve seen yet IRL? Neglecting planetary formation as a separate puzzle, how many small worlds can you jam together if you were to get a computer to solve this like the ‘eight queens’ problem?

    I am intrigued by this system’

    • David Ivory February 23, 2017, 2:20

      There’s a great thought experiment here on maximising the number of habitable planets in a solar system using earth sized planets & moons.


      Not incredibly scientific but a fun project.

      • Robert G February 24, 2017, 15:11

        Very interesting link, that. Thank you.

        Short answer is, in *very* contrived systems, dozens of small rocky worlds can be shoehorned into the habitable zones of their star. Packing multiple stars into a system again in a very artificial arrangement escalates the number up into the hundreds.

        In a naturally formed system, I guess Trappist 1 has to form our new ‘prior’ on the realistic upper limit: about 3. With moons of a gas giant, in possibly a few more.

        Once again, thanks for the link. A very interesting read.

  • Wojciech J February 22, 2017, 14:33

    It is also important to note that this system is very close on cosmic scale.
    Therefore such rich planetary systems could be quite widespread in the universe.
    This rises somewhat the chances of life in the universe(more planets where life could have formed).

  • RobFlores February 22, 2017, 14:35

    This Star and planets seems like our Jovian system, in terms organization, scaled up by an order of magnitude or two. Normally I refuse to get excited
    about M type stars and their planets. But this star is so weak, the orbits
    so small(and fast) , that a Nitrogen Atmosphere is likely to persist on world 1.2-1.4 RE. This would mitigate Some the Temperature Differential, if there is a large oceans the bonus is that it immediately becomes the most Earth like planetary world we know of, despite the flaring and x rays. How long any
    water lasts on the surface, well there’s the rub, but I think the world furthest
    from the star in the HZ is the preferred choice to keep H2O for a while.
    And Congratulations to us all. We have confirmation that Terrestrial worlds are not rare, I was not so sure before this finding.

  • Charley February 22, 2017, 14:40

    Astronomers discover 7 potentially habitable exoplanets orbiting nearby dwarf star

    An international team of astronomers has discovered seven potentially habitable exoplanets — or planets outside our solar system — that could have liquid water on their surfaces, according to a paper published Wednesday in the journal Nature.

    It is unclear whether any of the newly discovered planets can harbor life. However, scientists pointed out that the new planetary system orbits TRAPPIST-1, a dwarf star that is much younger than our sun and that will continue to burn for another 10 trillion years — more than 700 times longer than the universe has existed so far.

    Astronomers said that is “arguably enough time for life to evolve,” the article reported.

    TRAPPIST-1 is about 39 light-years away, in the constellation Aquarius.

    Astronomers noted, though, that they are awaiting the scheduled launch of NASA’s James Webb Space Telescope in 2018 to confirm what conditions — such as atmospheric composition and climate — are like on the exoplanets. The James Webb Space Telescope is expected to be significantly more powerful than the Hubble Space Telescope

    The discovery of the new planetary system has also indicated that Earth-sized planets are much more abundant and common in the Milky Way galaxy than previously thought, researchers said.

    The international team of astronomers that discovered the new exoplanets said they will be ramping up their efforts to locate and identify other planets around small stars in the vicinity of our sun through project Search for Habitable Planets Eclipsing Ultra-Cool Stars (SPECULOOS

    Additionally, NASA said it plans to launch the Transiting Exoplanet Survey Satellite (TESS), a space telescope that will spend two years finding planets orbiting over 200,000 of the brightest stars in the sky.


    • Ashley Baldwin February 22, 2017, 18:21

      Including the nearest 1000 red dwarfs which will include TRAPPIST- 1 . In just two years . Launched via a Falcon 9 Block 5 so with Space X’s recent travails and other priorities I understand that TESS has been pushed back till the early summer next year. The good news is that K2 should hold the transiting space telescope castle till then .Better still TESS has consumables for atleast five years ( and a durable satellite bus to match ) . So reaction wheels allowing it should gain a “high level review ” extension beyond its nominal mission and come close to matching its esteemed predecessor’s achievements . Just in time for PLATO……..Red dwarfs galore and some.

  • Andrew LePage February 22, 2017, 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.

    • Harry R Ray February 23, 2017, 10:36

      Andrew: That may still NOT be the case for MAIN SEQUENCE very late M stars. Please check out my comment from the latest posting on this website. This may make it even more difficult for you to give a thumbs up or a thumbs down to some of the other planets. ALSO: Please consider the fact that TRAPPIST-1h MAY be a Super-Europa-like object if its orbit is not circular.

  • Ashley Baldwin February 22, 2017, 15:04

    Habitability in this system is a moot point but what it represents further exciting evidence of the existence of multi terrestrial planetary systems around M dwarfs. WFIRST’s oft forgotten all planet microlensing study should help confirm if this is the norm. Yes if data to date by Kipping & Meadows et al is anything to go on. There are also many bigger, older and calmer M dwarf stars than tiny TRAPPIST-1 . Many having passed through their turbulent CME/ EUV ridden adolescence . Many of these will be assessed by TESS ( and K2/ PLATO) and will also have relatively deep and frequent transits which along with the longer wavelength near IR predominance, lends itself well to transit spectroscopy even extending down into the troposphere.

  • Harry R Ray February 22, 2017, 15:05

    Planet d could be the first REAL test of the “terminator” hypothesis. If you remember, on his ORIGINAL paper, Gillon mentioned that there was a very slim chance of habitability of b and c at the terminator. That idea was QUICKLY SQUASHED by theorists pointing out that they were almost certainly HOT water worlds. At less than 1/2 Earth mass, d is almost certainly NOT a water world NOW(although it may have ORIGINALLY been one). There is no way d can have an atmosphere THICK ENOUGH to efficiently TRANSPORT heat to the permanently tidally locked “night side”, allowing for temperate conditions at the terminator.

  • Marshall Eubanks February 22, 2017, 15:25

    Figuring out the basics of the atmospheres of these transiting planets is just a matter of collecting photons during transit (and eclipse, assuming that also happens) and using them wisely. Let’s hope they can find Oxygen.

  • DJ Kaplan February 22, 2017, 15:28

    I suppose it’s a matter of science journalists resisting the urge to translate “a planet in the habitable zone” to “habitable planet”. They are vastly different things as far as any of us know. The derivation of the product HZ remains the same, regardless of the type of star or its other qualities.

    • Ashley Baldwin February 26, 2017, 6:29

      True, but the old adage ” any publicity is good publicity” surely applies . This discovery has the potential for a domino effect. Revision of JWST’s observation prioritisation schedule for one . Then , and more importantly still, potential impact on the up coming NASA Decadel study . Not least the choice and instrument specification of any future space telescope and its observation priorities . As things stand there are 4 options with only 2, HabEx and LUVOIR suited to exoplanet work and one, an X-Ray telescope offering little potential. (exoplanets currently get just 10 % of JWST’s time , and this on a telescope primarily designed with longer IR observations of extra galactic targets in mind , though it’s unforeseen cost overrun has led to it being presented as a revisionist “Hubble 2” ) .

  • Marshall Eubanks February 22, 2017, 15:28

    Does anyone know if there are orbital resonances between these bodies? I have seen nothing about it, but my intuition says that they must be in an ordered relationship to be stable.

    • David Ivory February 23, 2017, 2:28

      From here: –


      These orbital interactions may have been key to stabilizing the TRAPPIST-1 system. The ratios of the time it takes for neighboring planets to orbit are all ratios of integers: 8/5, 5/3, 3/2, 3/2, and 4/3. Integer ratios provide interactions that help prevent the sort of planetary chaos that can launch planets out of the exosolar system or send them spinning into the host star. When we see resonances like this, it’s taken as a sign that the planets formed farther from their host star and migrated inward due to friction from the disk of material they formed within. Orbital resonances check this inward migration and produce tightly packed systems like TRAPPIST-1.

  • andy February 22, 2017, 15:35

    Did a quick check against a couple of mass-radius relationships, it looks like b and f have masses too low for terrestrial planets and therefore likely have significant fractions of ice in their composition. I’m also generally sceptical about the habitability prospects around fully-convective dwarf stars, but would be interesting to see what follow-up observations of this system reveal.

    • Ashley Baldwin February 26, 2017, 6:38

      Large ranges for mass , radius and thus density though so far given the limited number of recorded transits so far and their all important mass determining timing variations and durations . ( given TRAPPIST-1 is too small and dim for mass determination via conventional RV spectroscopy despite its relative proximity ) Incredibly fortuitously though, Kepler’s current near 3 month observation field 12 includes TRAPPIST-1 and will constrain the data significantly in adding around 130 more transits by early March.

  • Sean Robert Meaney February 22, 2017, 16:09

    What concerns me is the solar rotations of these planets. It takes us 365 days to roll around the Sun. These planets are doing that in 1/50th-1/100th the time. I always thought solar orbit speed of planets was related to the solar rotation velocity of the original debris cloud from which the planets form, and that would be based on the early life of the star as it formed a single mass. One solar mass has little reason to spin at great velocity, but two solar masses rolling around each other would.

  • jonW February 22, 2017, 16:15

    I was curious and just looked up the resolving power of a space telescope situated at the gravitational lens of the sun (550 AU away), to learn what it could expect to see on these planets around TRAPPIST-1. This quite nice article about some newish calculations https://www.technologyreview.com/s/601331/a-space-mission-to-the-gravitational-focus-of-the-sun/ says that at that distance (~30-40 ly) we could hope to see planetary details a mere kilometre across. However there are some complications described there that I hadn’t read about here before. Paul, maybe one day you could write a post with an update on astronomy near the sun’s gravitational focus?

    Another thought: imagine, if a civilisation did arise in this system, how tempting it would be for them to develop space-faring vessels, with so many worlds so close by. If our moon has provided a good incentive for mankind, think how much more eager a species would be to head out if they could visit two whole other planets at comparable distances to our moon. Maybe if life is common in the galaxy, it will be in these incentive-rich systems around very faint stars that we will first find species that have successfully left their own world.

    • Ashley Baldwin February 23, 2017, 16:53

      Earth equivalent insolation distance , EEID, expressed in milli arc seconds:
      EEID( mas) = 1000 ( square root of bolometric luminosity ( expressed as the ratio cf the Sun) all divided by distance in parsecs. ( Turnbull et al )

      A related equation for the conservative “habitable” zone applies across the range of 0.95 -1.4 X the root of the bolometric luminosity added to the above.

      WFIRST will have an inner imaging angle of 100mas at best . To cast things in perspective , Proxima b , with an intrinsically more luminous ( but still very dim M dwarf ) far nearer parent star ( 1.3 versus 12.3 parsecs ) and related wider habitable zone than TRAPPIST-1 , lies just at just 38 mas out.

      That’s a tough ask for direct imaging and ” day side” emission spectroscopy but with transmission ( night side ) spectroscopy possible by definition , all that is required is accurate transit timing and duration figures for each planet and observing and “binning” enough transit data to build up a reasonable spectrum.

      With short orbital periods even for the outer planets that should be possible though not quickly even for 6.5 m JWST given the low magnitude of the star even in the longer infrared bands its emits in .

  • Michael February 22, 2017, 16:21

    Can we name them after the seven dwarfs ; )

    • Ashley Baldwin February 22, 2017, 18:05

      Ha !
      I wouldn’t call crotchety TRAPPIST-1 “Snow White” though and it won’t even be “Snow White Dwarf” for several trillion years if ever .

      • Harry R Ray February 23, 2017, 10:53

        b-Chris Adams,c-Vin Tanner,d-Harry Luck, e-Bernardo O’Reilly, f-Britt, g-Lee, h-Chico; fro the ORIGINAL “The Magnificent Seven” movie. Of course, Harry Luck is my favorite planet, because, although not deemed habitable by most astronomers(and probably Andrew LePage as well, although we’ll have to wait and see about that)with a little LUCK(see my ABOVE COMMENT) there may be SOME life on very restricted areas of this world.

      • Brett Bellmore February 23, 2017, 21:47

        Shouldn’t at least one be named “Monk”?

    • Abelard Lindsey February 25, 2017, 0:04

      Snow red and the seven dwarfs.

      • Michael February 25, 2017, 14:06

        It is Snow white but she is having a terrible two thrombotic tantrum and the Dwarfs are trying to console her.

      • hiro February 25, 2017, 17:57

        Scarlet & 7 vampires or a little bit off Trapper & 7 nurses …. ah no, 7 (dirty) jokes/pranks.

  • hiro February 22, 2017, 16:25

    Planet g seems to be the most promising planet in this system; planet e & f might have atmosphere depletion over a period of couple billion years. The final one could be another quasi-Europa, it’s hard to tell but we need to examine Europa rigorously in near future in order to draw any useful conclusions about simple organisms living in water.

    • Sean Robert Meaney February 22, 2017, 18:35

      I wouldnt mind paying a dollar toward a probe designed to land on an outer planet and function as an observatory.

      • Ashley Baldwin February 23, 2017, 19:15

        Better still ( and cheaper ) a space telescope orbiting at either of the Sun/ Jupiter or better still Saturn Lagrange 2 points. Once the new megawatt advanced ROSAT-EX solar arrays can power it and with the availability of a suitable heavy launcher with upper stage to get it there in good order.

  • Phil February 22, 2017, 16:59

    We all know the caveats that seem to apply to red dwarf planets (although I’m not sure they are show stoppers) – what gives me pause here are the HUGE numbers of undiscovered planets that MUST still lie below the detection noise floors of other, closer, larger red dwarfs in our neighborhood. James Webb, TESS and new ground based instruments like GMT offer hope for a new golden age of discoveries in the next 10 years.

    In terms of this amazing little system, I’m interested if there has been any infrared excess found that might indicate a debris disk that might potentially supply ices to the inner system. Finally – that mass is painfully close to the hydrogen burning limit. Is there any chance that Trappist 1 is actually a very massive brown dwarf?


    • Ashley Baldwin February 22, 2017, 19:18

      The ESPRESSO high res spectrograph at the VLT, fully operational this year and the new bespoke planet hunting nearly as high res EXPRES spectrograph on the Discovery telescope ( as part of the “hundred Earths project” ) should also help find terrestrial planets around nearby M dwarfs. The latter particularly given its unique design feature of damping down chromospheric “noise” that so often interferes with the true Doppler signal for active stars.

      • Michael Fidler February 22, 2017, 22:23

        If NASA would get large funding for a exoplanets space telescope are there any feasible plans for it? Something in the 2.4 meter on up.

        • Ashley Baldwin February 23, 2017, 16:56

          4-6 m Habex ( Vis- NIR) is one of four next generation space telescopes undergoing feasibility ahead of the next Decadel study . Preliminary science definition team studies available on line.

          • Michael Fidler February 23, 2017, 21:59

            Thank you for the update, NASA has spent 9 billion on JWST so why destroy the team? How much in spare parts and equipment used to build JWST could be reused – look at the DOD having two spare 2.4 meter mirrors. Most large mirror making facilities churn out mirrors on a regular basis, for example the Steward Observatory Mirror Lab. Just imagine if we had 10 Hubble Telescopes in orbit what could be accomplished, there is never enough time on these scopes and it is extremely hard to get time on them. Like in Contact; S.R. Hadden: “First rule in government spending: why build one when you can have two at twice the price?”, or maybe cheaper by the dozen?
            Life detection capabilities of LUVOIR and HabEx

    • Bruce Mayfield February 23, 2017, 18:21

      There is a large chance that TRAPPIST-1 is a BD. No less an expert than Greg Laughlin pegs the RD:BD odds at 60:40.

    • Ashley Baldwin February 23, 2017, 19:20

      It’s spectrum and temperature imply hydrogen fusion . Though 80 Mjup is often listed as the cut off point the vagaries of hydrogen fusion at these “low” masses blur the Brown dwarf / low mass red dwarf boundary with some bodies as low as L2 V even being posited as main sequence stars .

  • Larry Kennedy February 22, 2017, 17:29

    Don’t I remember a paper not long ago indicating that planets in close proximity were less likely to be in tidal lock?

    • Bruce Mayfield February 24, 2017, 12:00

      Do you mean planets in close proximity to the star they orbit, or close proximity to each other? Tides increase with decreasing separation, so the closer to the star, the more likely tidal lock becomes.

      But as these worlds pass each other they will also tidally stretch each other, and very frequently too since the orbital periods are so fast. This will add to the internal heating they all experience.

      • Tulse February 24, 2017, 15:46

        Such internal heating might help mitigate somewhat the “eyeball” effect. And if the planet has a global ocean, would the tidal effect also help with heat transport on the dark side?

        • Bruce Mayfield February 24, 2017, 22:19

          Oceanic tides, if any oceans exist, could be quite large. Consider how large Earth’s tides can get when the Moon and Sun line up. Some of the distances between these orbits are not too much greater than the Earth/Moon distance, but all these bodies are much more massive than our Moon. Consider how big tides might get whenever all seven line up in a grand conjunction!

          These exo-earths could also have plenty of internal heat because of their youth, due to left over heat from accretion and more radioactive elements that haven’t had enough time to decay yet.

      • Larry Kennedy February 24, 2017, 19:52

        As I remember the paper was specifically referring to red dwarfs with planets in the habitable zone and the result of having other planets in close proximity.

    • Bruce Mayfield February 24, 2017, 12:10

      Just remembered that this kind of tidal stress/heating is what keeps Io so volcanically active. So several of these worlds could be very volcanic and tectonically active due to there effects on each other.

  • Ashley Baldwin February 22, 2017, 17:43

    Interesting the parallels between ” just a star ” TRAPPIST and Gas Giant Jupiter, not least the close “moon like ” proximity of the planets. I’m sure we will see something similar with brown dwarfs with orbiting bodies mid way in mass and distance . It has been posited for a while that there is a correlation between M dwarf mass and attendant planet size and this seems to extend all the way down to gas giants . Interesting to see if the orbital proximity is reflected in this too.

  • Coacervate February 22, 2017, 17:50

    Prof. Seager mentioned “Starshot”. Tau Zero’s star is rising

    • Paul Gilster February 22, 2017, 18:14

      I did hear her mention that, but do realize that Tau Zero isn’t the operating force behind Starshot. It’s the Breakthrough Initiative group. We’re just intensely interested in the effort and have collaborated a bit with them, as in the shared comments section for Starshot, linked at the top of the main page.

      • Coacervate February 23, 2017, 11:04

        the intersection of two sets then :)

  • Ken Marable February 22, 2017, 18:39

    I thought that in the press conference they did a good job of emphasizing that these are in the habitable zone only and that we don’t know much about them (like the comment about looking at our system, exoplanet astronomers would be amazed to find 3 planets in our habitable zone as well, or how saying that a good thing about this isn’t “look 3 habitable worlds” but “we have 3 chances in this system for a habitable world” – sorry, I’m paraphrasing from memory). Of course, we will see how science journalists oversimplify that, but it seemed that the researchers did a good job of emphasizing that.

    Also, am I wrong, or was 500 million years just given as the lower bound for the age of the star because the volatile period appears over?

  • RobFlores February 22, 2017, 19:06

    The Trappist-1 findings is a paramount moment in exploration, it opens
    the gate to lands suspected but now confirmed, to put in terms of the Age of Exploration on our planet, in the 15th and 16th century. And the exploration
    is just beginning….

    Looking at a list of Stars within 50 Light years of Earth,
    filtering for those which are from K9 to F6 type, star systems, that are singletons, it is something like 63 stars.

    The odds are with us (taking into account of Trappist_1 findings), that there is at least one world within 50 Ly, that is far more hospitable to life than ANY of the worlds discovered on Trappist-1. A world with a nitrogen atmosphere and active tectonics, where one could exists in a shirt sleeve environment, as long as you take into account the lack of OZONE in your excursion time. We need to think about the fastest way to find the jewels
    that may lie close to us, and obtain at least an amount of data to characterize
    them.(mass, radius,atmospheric make up, Water bodies, Continents) Unfortunately the technology of any probe used to explore Alpha Centauri will LIKELY be too slow, to explore give us Details of these worlds within a reasonable time span. Trappist-1 has shown the universe is not stingy
    about Near Terrestrial sized worlds, we only have to lift the veil obscuring them.

    • Malcolm Davis February 23, 2017, 3:35

      “A world with a nitrogen atmosphere and active tectonics, where one could exists in a shirt sleeve environment, as long as you take into account the lack of OZONE in your excursion time. ”

      Not to mention an alien and potentially hostile biosphere that somehow we’d have to be protected against. For the world to be habitable it cannot be biologically sterile – so all sorts of bugs and viruses and bacteria totally new to the human body would need to be detected, understood and neutralised.

      • RobFlores February 23, 2017, 12:02

        I wasn’t specific about it but, No Ozone meant that there is little or
        no free oxygen. Respirator required. Alien Bugs will have different
        biology. Non-compatible with earth life. Very inert with each other.

  • Joe February 22, 2017, 19:38

    With so many planets in close orbits about their star, I wonder what is the potential for collisions? Given that the star is only 500 million years old, perhaps there has not been time for collisions. It’s hard to see though how all these planet are going to orbit without collisions if you look out a few billion years.

    • SpaceKnight February 23, 2017, 6:24

      I’m no specialist, but with the resonances the orbits should be really stable once settled. (see Jupiter’s moons)

    • Daniel Högberg February 23, 2017, 9:46

      Joe, as a total amateur, that was my first thought too. It seems to me like the risk for collision is very high, potentially destroying any chances microbial ever life had? Maybe Im just plain wrong, and the planets are in very steady orbits. They age of the star and the system as a whole would of course play a key role in how stable the seven (or more) orbits are today. But then again, Im a total noob when it comes to extrasolar planetary science..

  • GatorALLin February 22, 2017, 23:50

    I hate to be negative in any way as I love that they keep finding rocky worlds that are about the size of the Earth, but please don’t confuse a rocky world that in within a habitable zone around a red dwarf or smaller star like this one. Note their orbits are just a few days vs. our 365 days… the mass of that star is like 8% of our sun… If you are serious about finding an Earth Like planet, you must start with a Sun like star… Of course the reason they are finding ones like this is they orbit in just a few days, so they show up quickly (vs. waiting 365 days and not being sure if it will blink it again, just imagine waiting for a Pluto …l0l). Anyhow…. No these planets won’t have life around them…. ever. unless we send it there and no we won’t be sending it there. They are burnt to a crisp on one side… frozen on the back side from being tidally locked. Think about this.. if there was life to every start up easily around a red dwarf… even a very small percentage of them. 1 of a billion for example, the Universe would be over spilling with life… but so far we find nothing.. (no Dyson Spheres, no objects moving at even 1/5 the speed of light anywhere, no energy usage that can’t be easily accounted for, no signals of any kind that could be intelligent based. Nothing.. Nada..Zilch. and so my common sense friends, you can bet your last bitcoin that there is no life around these, anymore than you can bake a real cake with a light bulb from 20 miles out. So here is the good news… we will know in about 20-30 years if there is life on any other planet or moon in our solar system and if nothing at all other than Earth, then that will say a lot about how silly an idea like panspermia is. Lets hope Webb telescope gets some hot finds going or places that at least seem to have a life possible atmosphere. Take every star in every galaxy and multiply it by 7 or 17… doesn’t really matter.. just divide that giant freaking number down by 1,000 just 12 times… it is less than zero. Are there 12 factors of 1/1000 that make Earth special? We don’t know of course, but there are likely a few that are just 1/10 and a few that are 1/billion. Maybe there are 50 that are 1/1000. or more. Start wondering if how our Earth was made with the giant impact theory (why we have this giant moon) and then wonder if two different planets that normally could never create life, mixed to be able to form life and thus that mix is a very rare combo of just the right chemicals and makes up just the right mass and atmophere, and tilt and spin and orbit and … x 1,000. OK the truth is we can’t yet even figure out how life started on earth to know how it could start anywhere else, so we still have a lot of homework to do here at home. Maybe we are just expecting to find life way, way too early at 13.7 from the start of the Big Bang. Could be that we are early by 1% of the endpoint of the universe (2 trillion years or so?). If a baby lives 100 years max lifespan.. why at age 7 months would you expect that baby to be doing anything of importance yet? That is what we are doing with intelligent life in the universe, or at least this galaxy… someone has to be first… and I am not saying for sure it is us… I am just saying that our ability to search more area and faster and different ways will continue to grow at a logarithmic scale and in 50 years from this email date, you still will not have heard a peep from the stars that allows us to confirm there are aliens out there (ones with radio towers or spaceships). It comes down to distance and time and limits of physics (no, I know you like all the cool star trek and holywood movies.. yeah me too. but they messed up your reality meter by a lot, or you were smoking that day vs. being in science class … All life that does not invent spaceships and use some Crispr9 to change their dna so much they can thrive in deep space will be lost forever and thus be of no value, or fail to pass on their knowledge and thus what is the point…? It is ALLin all life going to die off… unless.. unless they rise up and become gods. Start understanding what starshot means… exactly.. suddenly you realize your not going to be on any ships… nothing more than a postage stamp will get up to 20% the speed of light.. our great filter may prove that living stuff is heavy and hard to move and survive in speed space… so maybe we don’t get to go.. maybe we are just one of many stepping stones for the life or the machine or the “not sure what to call it” that gets to offset that awful waste of space. it seems to be that or nothing… I take that over nothing any day. We have lots of time before our sun heats up just s tiny bit to boil off all our oceans.. and just maybe someone else said the same thing and then Ding.. hit by a big old rock from space (hey we have Jupiter, so maybe why we are still here). I hope they do find something and soon… (Yeah, I know Nick Bostrom does not want to find it due to fear of the great filter being ahead of us.. I think there are lots of small and medium great filters.. plus distance, time and we are stuck with these laws of physics and the gap to what the movies make us wish we had is too huge).

  • Neil S February 23, 2017, 0:03

    Here’s an article in Ars Technica with discussion about resonance and stability just below the animation. It suggests there is stability enhanced by the closeness. I vouch for nothing.


  • Clark L. Zeuss February 23, 2017, 0:14

    The one tidbit from the announcement that I latched onto was the comment that we are in the “gold rush” era of exoplanet discovery. They mentioned SPECULOOS and its potential to find hundreds of more stars like TRAPPIST-1. This is almost certainly going to be an exciting time of one big discovery after another.

  • Phil February 23, 2017, 2:49

    I wonder if future RV or TTV studies might find MORE planets around this star exterior to those announced that don’t transit? How many planets can a star have? (I guess it has something to do with the size of the protostellar disk?)


    • Bruce Mayfield February 23, 2017, 16:31

      Further studies are quite likely to find even more planets orbiting TRAPPIST-1, I would think. (Heck, we haven’t even finished counting up all the planets in our own system yet.) RV & TTV work could be very fruitful here since the system is so nearly perfectly aligned with us. Even additional transiting planets might be found with longer observations, although the odds of a transit drop with distance.

      “How many planets can a star have?” A great question Phil. This discovery might suggest a continuum between giant planets and the smallest stars. Think about how many moons our ice and gas giants have!


  • Mauldred February 23, 2017, 4:14

    If we do the math, we find for Trappist-1 e a surface gravity of approximately 0.73 g, however the error margin is quite big, more than +/- 0.4 g (as the mass is known with an error margin of +/- 0.58 M⊕). In any case that’s a comfortable surface gravity to retain an Earth-like atmosphere, if the planet has a sufficiently strong magnetic field to resist Trappist-1’s solar wind and flares.

    I like the idea from Michael Gillon to name the Trappist-1 planets after famous Belgian trappist beers.

    “Mr Sulu, set a course for Achel Blonde, so we can study the Trappist system from within the habitable zone without being detected by the sentient creatures on Chimay Triple!”

    • Paul Gilster February 23, 2017, 10:06

      “Mr Sulu, set a course for Achel Blonde, so we can study the Trappist system from within the habitable zone without being detected by the sentient creatures on Chimay Triple!”

      Love it. I absolutely endorse this idea about the naming of the TRAPPIST-1 planets!

      • Tulse February 23, 2017, 10:36

        We might be hard-pressed to use solely Trappist beers, but with Belgians we could do:


        • Ronald February 25, 2017, 8:29

          Yes and no: I am all for naming them after Trappist beer breweries, but your names are (partly) wrong. In a moment I will come up with a suggesties, the names of the official 6 Belgian and 1 Dutch Trappist breweries.

    • Michael February 23, 2017, 14:49

      A seven pub crawl is doable, but seven planets me thinks not!

      As for intellegent life in this system I suspect they may be trapped-and-pist.

  • xcalibur February 23, 2017, 5:20

    This is a huge find. It confirms my judgment that terrestrial planets are fairly common in the universe.

    As for habitability, we have data right here in this solar system. Of our terrestrial planets, only Earth is habitable. Venus and Mars may have once been habitable, but Venus had a runaway greenhouse effect while Mars had its atmosphere stripped to become a cold desert. Mercury was always a burning/freezing rock, while Ceres is a super-asteroid.

    This suggests to me that habitability, while not unique to Earth, can be precarious.

  • Nicolas AUGUST February 23, 2017, 5:50

    All theses Earth sized planets around a single star is indeed a great news for the potential number of such planets in the Galaxy.

    The stability of this system could be good if we think of it as a Jupiter like system (Trappist 1 is not very different from a super Jupiter and its planets form in a way a bigger and larger version of the Jovian family).

    • Bruce Mayfield February 23, 2017, 16:44

      Tens of trillions of terrestrial worlds in the Milky Way perhaps?

  • Robert Feyerharm February 23, 2017, 14:38

    I plotted the mass and radius of the TRAPPIST-1 worlds plus our own Solar system’s four terrestrial planets in Excel, with vertical & horizontal error bars.

    It’s interesting to see how well a logarithmic curve fits the eleven data points, with an approximate formula of Radius = 0.2343 x ln(Mass) + 1.0329.

    TRAPPIST-1f appears to have an unusually large radius (1.045 +/- 0.038 Earth units) despite its low mass of 0.68 +/- 0.18 Earth units.

  • Robert Feyerharm February 23, 2017, 14:55

    BTW the Nature article “Seven temperate terrestrial planets around the
    nearby ultracool dwarf star TRAPPIST-1” is available on the Nature website by clicking on Reference 1 at the bottom of the page (although it cannot be downloaded without paying):


  • Michael Fidler February 24, 2017, 2:05

    ‘Quartz’ crystals at the Earth’s core power its magnetic field.
    So how will this effect the models for the planets at TRAPPIST-1?

  • Michael Fidler February 24, 2017, 2:12

    Venus’s 583.92-day interval between successive close approaches to Earth is equal to 5.001444 Venusian solar days, making approximately the same face visible from Earth at each close approach. Whether this relationship arose by chance or is the result of some kind of tidal locking with Earth is unknown.

  • Michael Fidler February 24, 2017, 3:11

    TRAPPIST-1 b and c are only 300,000 miles apart at opposition/inferior conjunction; c and d 550,000 miles; d and e 650,000 miles; e and f 800,000 miles and so on . There has to be a lot of torque from each other as they pass nearby, b and c are almost as close as our moon is to earth! Does anyone know of a good program for calculating the opposition/conjunctions of multi exoplanet solar systems? The program from NASA “Eyes on Exoplanets” could work but the orbital period and mass for the TRAPPIST-1 planets are incorrect!

    The complex planetary synchronization structure of the solar

    • Bruce Mayfield February 24, 2017, 12:30

      With these worlds passing so close to each other, if any of them have large oceans they would definitely experience large tides.

  • Harry R Ray February 26, 2017, 15:03

    Oh boy! Surf’s up on steroids(assuming they are not entirely covered by water and there are a few beaches around)!