≡ Menu

TRAPPIST-1h: Filling in the Picture

One of the worst things we can do is to get so wedded to a concept that we fail to see conflicting information. That’s true whether the people involved are scientists, or stock brokers, or writers. It’s all too easy to distort the surrounding facts because we want to get a particular result, a process that is often subtle enough that we don’t notice it. Thus I was interested in what Rodrigo Luger said about his recent work on the outermost planet of TRAPPIST-1:

“It had me worried for a while that we were seeing what we wanted to see. Things are almost never exactly as you expect in this field — there are usually surprises around every corner, but theory and observation matched perfectly in this case.”

And that’s just it — in exoplanet research, we’ve come to expect the unexpected. So when Luger (a doctoral student at the University of Washington) went to work on this intriguing star some 40 light years from Earth, and its seven now famous planets, he was understandably edgy. Would TRAPPIST-1h turn out to orbit just where his team had projected?


Image: A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres. Credit: NASA/R. Hurt/T. Pyle.

You’ll recall that it was the original survey led by Michaël Gillon (University of Liège, Belgium) that identified three planets around TRAPPIST-1 in 2016, a number that jumped to seven in a 2017 paper that drew worldwide attention, especially because several of the planets appeared to be within the star’s habitable zone. TRAPPIST-1h was a problem because Gillon and team were only able to observe a single transit. What Luger proceeded to do, working with Gillon as one of his co-authors, was to follow up on that work with an international effort that studied 79 days of K2 data, snaring four transits of TRAPPIST-1h in the process.

The bit about seeing what you want to see comes from the fact that the planets of TRAPPIST-1 are locked into an orbital resonance, making their orbital periods mathematically related. Luger and colleagues wanted to use the orbital velocities of the better understood TRAPPIST-1 planets to make a prediction about the orbital velocity and period of TRAPPIST-1h. Six possible resonant periods for the planet came out of these calculations, but subsequent data ruled out all but one. Would resonance unlock the problem?

The answer was yes. The K2 data confirmed the prediction, showing us that TRAPPIST-1h is in a frigid 18.77 day orbit around the ultracool dwarf star. At this distance from the host, the planet receives about as much energy per unit area from its star as Ceres receives from the Sun.

Image: The animation shows a simulation of the planets of TRAPPIST-1 orbiting for 90 Earth-days. After 15 Earth-days, the animation focuses only on the outer three planets: TRAPPIST-1f, TRAPPIST-1g, TRAPPIST-1h. The motion freezes each time two adjacent planets pass each other; an arrow appears pointing to the location of the third planet. This complex but predictable pattern, called an orbital resonance, occurs when planets exert a regular, periodic gravitational tug on each other as they orbit their star. The three-body resonance of the outer three planets causes the planets to repeat the same relative positions, and expecting such a resonance was used to predict the orbital period of TRAPPIST-1h. Credit: Daniel Fabrycky/University of Chicago.

So now we have a seven-planet chain of resonances. We’ve seen other multi-planet resonances — four-planet resonances exist at Kepler-80 and Kepler-223 — but TRAPPIST-1, as in so many things, ups the ante considerably. The resonance picture here also gives us ideas about the history of this system, which is thought to be somewhere between 3 billion and 8 billion years old (and if that range of possibilities isn’t a reminder of how much we have to learn about dating cool stars like this, I don’t know what is).

From the paper:

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.

Thus we’re looking at possible migration inward of a set of planets that migrated in what Luger calls ‘lock-step.’ Suddenly TRAPPIST-1 becomes an excellent test case not only for planet formation but planet migration theories. The paper continues:

This model matches the observed period ratio distribution of adjacent super-Earths if the vast majority (∼ 90%) of resonant chains become unstable and undergo a phase of giant impacts. Some resonant chains do survive, and a handful of multiple-resonant super-Earth systems have indeed been characterized. The TRAPPIST-1 system may thus represent a pristine surviving chain of mean motion resonances.

This would have been, the authors believe, a slow migration given the low mass of the TRAPPIST-1 planet-forming disk, and the fact that the planets themselves are low in mass. Perhaps this explains why the TRAPPIST-1 resonant chain is less compact than in systems with more massive planets, and why its unique stability has survived.

And what more can I say about K2? Despite everything going against the TRAPPIST-1h work, including not just the drift and jitter of the spacecraft in its less than optimum state but the faintness of the occasionally flaring target, K2 nonetheless delivered the goods. It’s a real testimony to those working the mission that we’re still pulling useful data out of the K2 observations, and testimony as well to the quality of the team working TRAPPIST-1h.

The paper is Luger et al.,”A seven-planet resonant chain in TRAPPIST-1,” Nature Astronomy 1 (2017), 0129 (abstract / preprint).


Comments on this entry are closed.

  • Paul Topping May 23, 2017, 13:45

    My question is not about the TRAPPIST-1 system per se but I suspect some of the people who read these comments can point me to the answer. What are the chances of planetary systems like TRAPPIST-1 having their orbital plane being edge-on to us? Are they most likely to match that of the stars orbiting in the Milky Way? If there are nearby planetary systems where the planets do not transit their star, would we know about them at all? I suppose star wobble is still detectable but only for very large planets.

    • Harry R Ray May 23, 2017, 17:03

      The TRAPPIST telescope observed around 60 stars similar to TRAPPIST-1. SO: The current BEST ESTIMATE RIGHT NOW would be one in sixty to one standard deviation. ALSO: The Titus-Bode Law is back, BIG-TIME. David Kipping predicted the DISTANCE of TRAPPIST-1h from TRAPPIST-1 LONG BEFORE Luger predicted the orbital period using this “outdated” method that was long ago “discredited” and summarily DISCARDED into the scientific method “trash bin”! Kipping even predicted TRAPPIST-1i at the NEXT Titus-Bode distance. I have a GUT FEELING that TRAPPIST-1i DOES exist, but is Mars-sized or SMALLER! Because of its DIMINUATIVE SIZE, it did NOT SHOW UP in the rough, UNPROCESSED K2 data! Hopefully, in just a few days(i.e. SOMETIME BEFORE June 1)when the processed, HIGHLY CALIBRATED Campaign 12 data is released, Luger et al, MAY be able to TEASE TRAPPIST-1i out of the better data, ESPECIALLY NOW THAT THEY KNOW PRECISELY WHERE TO LOOK!!! I hope they TRY!!! If TRAPPIST-1i IS found, OTHER PLANETS that were either MISSING because they were transiting DURING the five-day “safe-mode” interval, or whose orbital periods are LONGER than the Campaign 12 71 day time span, or maybe JUST DO NOT TRANSIT could exist as well and be teased out via TTV RESIDUALS of the inner 7 planets now that we have such PRECISE KNOWLEDGE of BOTH the distances AND the orbital periods of ALL 7!

  • Michael C. Fidler May 23, 2017, 19:56

    Fascinating reading – Harry R Ray do you have some links for Kipping?

    Some more predictions!

    Exoplanet Predictions Based on Harmonic Orbit Resonances.
    Markus J. Aschwanden, Felix Scholkmann
    The current exoplanet database includes 5454 confirmed planets and candidate planets observed with the KEPLER mission. We find 932 planet pairs from which we extract distance and orbital period ratios. While earlier studies used the Titius-Bode law or a generalized version with logarithmic spacing, which both lack a physical model, we employ here the theory of harmonic orbit resonances, which contains quantized ratios instead, to explain the observed planet distance ratios and to predict undetected exoplanets. We find that the most prevailing harmonic ratios are (2:1), (3:2), and (5:3), in 73\% of the cases, while alternative harmonic ratios of (5:4), (4:3), (5:2), (3:1) occur in 27\% of the other cases. Our orbital predictions includes 171 exoplanets, 2 Jupiter moons, one Saturn moon, 3 Uranus moons, and 4 Neptune moons. The accuracy of the predicted planet distances amounts to a few percent, which fits the data significantly better than the Titius-Bode law or a logarithmic spacing. This information may be useful for targeted exoplanet searches with Kepler data and to estimate the number of live-carrying planets in habitable zones.


    • Harry R Ray May 24, 2017, 9:51

      Thanks for the heads up! I posted a comment on this website a few weeks ago mentioning that the Kepler 186 system has a resonance chain similar to that of TRAPPIST-1. At that time I did not know how many more planets would be needed to COMPLETE the chain. According to this paper, 3 more are needed. One would be in the OPTOMISTIC habitable zone(like TRAPPIST-1d)very near the inner edge of the CONSERVATIVE habitable zone. The other two would be right in the MIDDLE of the CONSEVATIVE habitable zone. This is one MORE planet than the two Sean Raymond predicted. As for David Kipping, what I do is google David Kipping, click the Twitter feed on the list page. you would then have to scroll down to the appropriate tweets. Welcom to the age of Twitter Science!

    • Michael C. Fidler May 30, 2017, 22:36

      On the Spin States of Habitable Zone Exoplanets Around M Dwarfs: The Effect of a Near-Resonant Companion.

      “One longstanding problem for the potential habitability of planets within M dwarf systems is their likelihood to be tidally locked in a synchronously rotating spin state. This problem thus far has largely been addressed only by considering two objects: the star and the planet itself. However, many systems have been found to harbor multiple planets, with some in or very near to mean-motion resonances. The presence of a planetary companion near a mean-motion resonance can induce oscillatory variations in the mean-motion of the planet, which we demonstrate can have significant effects on the spin-state of an otherwise synchronously rotating planet. In particular, we find that a planetary companion near a mean-motion resonance can excite the spin states of planets in the habitable zone of small, cool stars, pushing otherwise synchronously rotating planets into higher amplitude librations of the spin state, or even complete circulation resulting in effective stellar days with full surface coverage on the order of years or decades. This increase in illuminated area can have potentially dramatic influences on climate, and thus on habitability. We also find that the resultant spin state can be very sensitive to initial conditions due to the chaotic nature of the spin state at early times within certain regimes. We apply our model to two hypothetical planetary systems inspired by the K00255 and TRAPPIST-1 systems, which both have Earth-sized planets in mean-motion resonances orbiting cool stars”.


      What is interesting is that we have two types of trees that are capable of surviving in cold and low light conditions: Deciduous and Coniferous trees. I often wondered if these types of trees may be common on exoplanets, since long nights and cold WX seems to be more likely on rocky exoplanets. Could ours trees have passed from other planets via seeds thru panspermia? [life being passed around thru space via asteroids and comets] Should we be looking for these types of forest and seasonal changes on exoplanets with the new instruments coming online?

      • Alex Tolley May 31, 2017, 13:54

        Could ours trees have passed from other planets via seeds thru panspermia?

        Stage trees? (Niven’s Known Space)

        • Michael C. Fidler June 1, 2017, 3:15

          Good point, what about pine cones and other plant seeds being ejected from the pods, (I think this also happens when forest fire occur) just how much would it take for small seeds to be launched into orbit? What about severe tidal waves on TRAPPIST 1 when the planetary alignments occur? Water + Seeds + Dirt = COMETS! Hmm, Just have a low density water world with some land and impacts from other nearby planets!


          • Harry R Ray June 1, 2017, 11:10

            Extrapolating from Figure A1 of this paper, here are the revised(IN SOME CASES ONLY)surface temperatures(CODE: stellar radiation only/tidal dissipation added). TRAPPIST-1b 402K/402K; TRAPPIST-1c 345K/345K; TRAPPIST-1d 285K/330K; TRAPPIST-1e 250K/275K; TRAPPIST-1f 220K/235K; TRAPPIST-1g 180K/180K; TRAPPIST-1f 168K/168K. This would take TRAPPIST-1d(formally in the optimistic habitable zone)OUT of the habitable zone ALTOGETHER! TRAPPIST-1e would move from the middle of the concervative habitable zone to either the VERY INNER PART of the conservative habitable zone or the optimistic habitable zone(I will let Andrew LePage make the final call on THAT ONE). TRAPPIST-1f would move from the outer part of the conservative habitable zone(where a recent climatological model stated that it would freeze over entirely if it were an “ocean world”) to the middle of the conservative habitable zone(where, PRESUMABLY, this would NOT happen).

            • Harry R Ray June 1, 2017, 11:11

              Sorry, I meant TRAPPIST-1h 168K/168K>

              • Michael C. Fidler June 3, 2017, 7:05

                I was looking at the temperature ranges for these planets and found some very interesting articles!

                Requirements and limits for life in the context of exoplanets.
                Christopher P. McKay

                Ecological limits to life

                Parameter Limit Note
                Lower temperature ∼ −15 °C Limited by liquid water associated with thin films or saline solutions
                Upper temperature 122 °C Solubility of lipids in water, protein stability
                Maximum pressure 1,100 atm Ref. 10
                Low light ∼0.01 μmol m−2⋅s−1 = 5 × 10−6 direct sunlight Algae under ice and deep sea
                pH 0–12.5
                Salinity Saturated NaCl Depends on the salt and temperature
                Water activity 0.6 Yeasts and molds
                0.8 Bacteria
                UV ≥1,000 J m−2 D. radiodurans
                Radiation 50 Gy/h D. radiodurans growth with continuous dose
                12,000 Gy Acute dose, higher for dry or frozen state
                Modified from ref. 2; UV and radiation entries from ref. 42.

                • Michael C. Fidler June 3, 2017, 7:12

                  More From: Requirements and limits for life in the context of exoplanets.

                  Temperature, Cold Limit.
                  “Many organisms can grow and reproduce at temperatures well below the freezing point of pure water because their intracellular material contains salts and other solutes that lower the freezing point of the solution. Recently, Mykytczuk et al. (20) reported an isolate from Arctic permafrost that grows and divides at −15 °C, the lowest temperature demonstrated to date, and is metabolically active at −25 °C in frozen soils. Thin films of water at the interface between ice and soil grains, augmented by any solutes, provide adequate water for life at these low temperatures (20, 21). The snow algae Chlamydomonas nivalis thrives in liquid water associated with snow, coloring it red, but the algae are the beneficiaries of external processes that melt the snow (22, 23). Microbial activity can generate sufficient heat in permafrost soils (and landfills and composts) such that it is a major contributor to melting (24, 25), but there is no known occurrence of an organism using metabolic energy coupled directly, e.g., through enzymes, to overcome the latent heat of fusion of ice thereby liquefying it.”

                  Temperature, Hot Limit.
                  “Many of the exoplanets discovered to date have high surface temperatures and hence the high-temperature limit of life is of particular interest. Takai et al. (8) showed growth, survival, and methane production by a methanogen at 122 °C where the high pressure (20 MPa, ∼200 atmospheres) stabilized the liquid water. At higher pressure water can be liquid at even higher temperatures. However, as water is heated and maintained as a liquid under pressure, the dielectric constant and the polarity of the liquid decreases sharply, thus significantly changing its characteristics as a solvent and its interaction with dissolved biomolecules, in particular lipids, but also proteins and nucleic acids. At 200 °C the dielectric constant is about half of the room temperature value (26). It is likely that the destabilization of lipid bilayers as they become soluble in the lower dielectric constant water is what sets the high-temperature limit on life. It is therefore perhaps not surprising that the organisms that can survive the highest temperatures are archaea (8, 27), as their membrane lipids are held together with ether bonds, which are chemically more resistant than ester bonds, which are used in the membranes of nonarchaea. Denaturing of proteins with temperature appears also to play a role (28). Hot water in contact with rocks can be efficient in generating or recycling redox couples––this has been suggested for the interior of Enceladus (29). Such ecosystems provide a compelling example of possible life below the ocean of an exoplanet or exomoon and can even be productive enough to support multicellular life––in the presence of an O2-rich environment.”

                  UV and Radiation.
                  “Complex life forms (such as humans) are sensitive to radiation but the dose that can be tolerated by many microorganisms is astonishingly high given natural levels of radiation in the environment. Table 3 lists the tolerances and acute dose survival for Deinococcus radiodurans, a well-studied soil heterotroph with high radiation tolerance (42). It has been suggested that the high radiation tolerance of D. radiodurans is due to adaptation to dehydration stress (43). Desert cyanobacteria of the genus Chroococcidiopsis (shown in their characteristic hypolithic growth form in Fig. 3B) are extremely resistant to desiccation, ionizing radiation, and UV (44, 45). An exoplanet would not require a magnetic field to be habitable. Any plausible field would not deflect galactic cosmic rays because these particles are much too energetic. These particles are primarily stopped by the mass of the atmosphere or surface materials. The column mass Earth’s atmosphere is equivalent to 1 kg/cm2. The Earth’s magnetic field does deflect solar protons channeling these particles to the polar regions creating the aurora. However, even without the magnetic field these particles would not penetrate the Earth’s atmosphere and would not reach the surface. Earth occasionally loses its strong dipole field during field reversals. These events are not correlated with extinctions in the fossil record.”

                  Very interesting reading and surprising about the temperature life can survive under high pressure in water.

  • Michael C. Fidler May 23, 2017, 21:46

    Some interesting articles that smack of earthly Chauvinism!

    The Drake Equation as a Function of Spectral Type and Time.
    Jacob Haqq-Misra, Ravi Kumar Kopparapu
    This chapter draws upon astronomical observations and modeling to constrain the prevalence of communicative civilizations in the galaxy. We discuss the dependence of the Drake equation parameters on the spectral type of the host star and the time since the galaxy formed, which allow us to examine trajectories for the emergence of communicative civilizations over the history of the galaxy. We suggest that the maximum lifetime of communicative civilizations depends on the spectral type of the host star, which implies that F- and G-dwarf stars are the best places to search for signs of technological intelligence today.

    Why do we find ourselves around a yellow star instead of a red star?
    Jacob Haqq-Misra, Ravi Kumar Kopparpu, Eric T. Wolf
    M-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. In this paper we analyze this problem through Bayesian inference to demonstrate that our occurrence around a G-dwarf might be a slight statistical anomaly, but only the sort of chance event that we expect to occur regularly. Even if M-dwarfs provide more numerous habitable planets today and in the future, we still expect mid G- to early K-dwarfs stars to be the most likely place for observers like ourselves. This suggests that observers with similar cognitive capabilities as us are most likely to be found at the present time and place, rather than in the future or around much smaller stars.

    But I beg to differ and here is why:
    One aspect that is not taken into account in the “Drake Equation” and its reliance on the Earth and Sun as the “Crown of Creation” is a very simple problem in statistics!

    The total solar eclipse of the sun, we are in a lucky position of having our moon 400 times smaller and the sun 400 time further away from our perspective on earth. This unique occurrence will only last for a short period as the moons orbit slowly moves further out from earth and all solar eclipses become annular eclipses. ( I could use some help as to how long the time period will last.) Now just how rare would it be in the galaxy to have a intelligent civilization develop when this coincidence occurs ? Since this does not occur anyplace else in the solar system entourage of planets and moons and only occurs where the sun and moon is the largest in the planets sky plus at the edge of planets that are tidally-locked to the sun seems to indicate just how rare it would occur in solar type stars. The problem is that reducing the chance for intelligent civilizations to just stars similar to the sun makes this occurrence even more unlikely! Looking at natures ability to defy the laws of statistics and create so many unusual and strange things in this universe I would have to say that M and K type stars are much more likely to have intelligent life on there given there larger numbers and greater age then solar type stars.
    “Just waiting to see the black hole in the sky on August 21, 2017”

  • Harry R Ray June 8, 2017, 10:09

    There is a new paper up on the Exoplanet.eu website that changes EVERYTHING! “On the Age of the TRAPPIST-1 system”. by Adam J Burgasser(UCSD)Eric E. Mamajic(JPL/Caltech/U Rochester. TRAPPIST-1 is 7.6+/- 2.2 Gyear, SLIGHTLY(compared to our sun)metal rich(Fe/H=0.06), and the BIG CHANGE is an approximately 10% INCREASE in radius(from 0.114Rs to 0.121Rs)! This means that all of the planets would ALSO have slightly LARGER radiii, too(b:1.1846Re, c:1.1616Re, d:0.8492Re, e: 1.0098Re, f: 1.1495Re, g: 1.2397Re, and h: 0.8272Re)! ALSO; a little OT, but the first FREE-FLOATING binary planet has been CONFIRMED! 2MASS J1193254-1137466A-B BOTH have masses 0f 3.7(+1.2,-0.9)Mj! They orbiy each other in an orbital period of 90(+80,_50 years at an AVERAGE distance of 3.6 AU.