TRAPPIST-1 - so much data, it all goes here

[Roger E. Moore]

TRAPPIST-1, the only known planetary system with seven terrestrial worlds, packed together like eggs in a box around a red dwarf star. Latest information, more to come no doubt.....


https://arxiv.org/abs/1802.05034

Cometary impactors on the TRAPPIST-1 planets can destroy all planetary atmospheres and rebuild secondary atmospheres on planets f, g, h

Quentin Kral, Mark C. Wyatt, Amaury H.M.J. Triaud, Sebastian Marino, Philippe Thebault, Oliver Shorttle
(Submitted on 14 Feb 2018 (v1), last revised 3 Jul 2018 (this version, v2))

The TRAPPIST-1 system is unique in that it has a chain of seven terrestrial Earth-like planets located close to or in its habitable zone. In this paper, we study the effect of potential cometary impacts on the TRAPPIST-1 planets and how they would affect the primordial atmospheres of these planets. We consider both atmospheric mass loss and volatile delivery with a view to assessing whether any sort of life has a chance to develop. We ran N-body simulations to investigate the orbital evolution of potential impacting comets, to determine which planets are more likely to be impacted and the distributions of impact velocities. We consider three scenarios that could potentially throw comets into the inner region (i.e., within 0.1 au where the seven planets are located) from an (as yet undetected) outer belt similar to the Kuiper belt or an Oort cloud: Planet scattering, the Kozai-Lidov mechanism and Galactic tides. For the different scenarios, we quantify, for each planet, how much atmospheric mass is lost and what mass of volatiles can be delivered over the age of the system depending on the mass scattered out of the outer belt. We find that the resulting high velocity impacts can easily destroy the primordial atmospheres of all seven planets, even if the mass scattered from the outer belt is as low as that of the Kuiper belt. However, we find that the atmospheres of the outermost planets f, g and h can also easily be replenished with cometary volatiles (e.g. ∼ an Earth ocean mass of water could be delivered). These scenarios would thus imply that the atmospheres of these outermost planets could be more massive than those of the innermost planets, and have volatiles-enriched composition.

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https://arxiv.org/abs/1808.08377

Detectability of biosignatures in anoxic atmospheres with the James Webb Space Telescope: A TRAPPIST-1e case study

Joshua Krissansen-Totton, Ryan Garland, Patrick Irwin, David C. Catling
(Submitted on 25 Aug 2018)

The James Webb Space Telescope (JWST) may be capable of finding biogenic gases in the atmospheres of habitable exoplanets around low mass stars. Considerable attention has been given to the detectability of biogenic oxygen, which could be found using an ozone proxy, but ozone detection with JWST will be extremely challenging, even for the most favorable targets. Here, we investigate the detectability of biosignatures in anoxic atmospheres analogous to those that likely existed on the early Earth. Arguably, such anoxic biosignatures could be more prevalent than oxygen biosignatures if life exists elsewhere. Specifically, we simulate JWST retrievals of TRAPPIST-1e to determine whether the methane plus carbon dioxide disequilibrium biosignature pair is detectable in transit transmission. We find that ~10 transits using the Near InfraRed Spectrograph (NIRSpec) prism instrument may be sufficient to detect carbon dioxide and constrain methane abundances sufficiently well to rule out known, non-biological CH 4 production scenarios to ~90% confidence. Furthermore, it might be possible to put an upper limit on carbon monoxide abundances that would help rule out non-biological methane-production scenarios, assuming the surface biosphere would efficiently drawdown atmospheric CO. Our results are relatively insensitive to high altitude clouds and instrument noise floor assumptions, although stellar heterogeneity and variability may present challenges.

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https://arxiv.org/abs/1807.10835

Predicting the Orbit of TRAPPIST-1i

David Kipping
(Submitted on 27 Jul 2018)

The TRAPPIST-1 system provides an exquisite laboratory for advancing our understanding exoplanetary atmospheres, compositions, dynamics and architectures. A remarkable aspect of TRAPPIST-1 is that it represents the longest known resonance chain, where all seven planets share near mean motion resonances with their neighbors. Prior to the measurement of 1h's period, Luger et al. (2017) showed that six possible and highly precise periods for 1h were expected, assuming it also participated in the resonant chain. We show here that combining this argument with a Titius-Bode law fit of the inner six worlds narrows the choices down to a single precise postdiction for 1h's period, which is ultimately the correct period. But a successful postdiction is never as convincing as a successful prediction, and so we take the next step and apply this argument to a hypothetical TRAPPIST-1i. We find two possible periods predicted by this argument, either 25.345 or 28.699 days. If successful, this may provide the basis for planet prediction in compact resonant chain systems. If falsified, this would indicate that the argument lacks true predictive power and may not be worthwhile pursuing further in our efforts to build predictive models for planetary systems.

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https://arxiv.org/abs/1808.01803

Interior characterization in multiplanetary systems: TRAPPIST-1

Caroline Dorn, Klaus Mosegaard, Simon L Grimm, Yann Alibert
(Submitted on 6 Aug 2018)

Interior characterization traditionally relies on individual planetary properties, ignoring correlations between different planets of the same system. For multi-planetary systems, planetary data are generally correlated. This is because, the differential masses and radii are better constrained than absolute planetary masses and radii. We explore such correlations and data specific to the multiplanetary-system of TRAPPIST-1 and study their value for our understanding of planet interiors. Furthermore, we demonstrate that the rocky interior of planets in a multi-planetary system can be preferentially probed by studying the most dense planet representing a rocky interior analogue. Our methodology includes a Bayesian inference analysis that uses a Markov chain Monte Carlo scheme. Our interior estimates account for the anticipated variability in the compositions and layer thicknesses of core, mantle, water oceans and ice layers, and a gas envelope. Our results show that (1) interior estimates significantly depend on available abundance proxies and (2) that the importance of inter-dependent planetary data for interior characterization is comparable to changes in data precision by 30 %. For the interiors of TRAPPIST-1 planets, we find that possible water mass fractions generally range from 0-25 %. The lack of a clear trend of water budgets with orbital period or planet mass challenges possible formation scenarios. While our estimates change relatively little with data precision, they critically depend on data accuracy. If planetary masses varied within ~24 %, interiors would be consistent with uniform (~7 %) or an increasing water mass fractions with orbital period (~2-12 %).

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https://arxiv.org/abs/1808.02808

Non-detection of Contamination by Stellar Activity in the Spitzer Transit Light Curves of TRAPPIST-1

Brett M. Morris, Eric Agol, Leslie Hebb, Suzanne L. Hawley, Michaël Gillon, Elsa Ducrot, Laetitia Delrez, James Ingalls, Brice-Olivier Demory
(Submitted on 8 Aug 2018)

We apply the transit light curve self-contamination technique of Morris et al. (2018) to search for the effect of stellar activity on the transits of the ultracool dwarf TRAPPIST-1 with 2018 Spitzer photometry. The self-contamination method fits the transit light curves of planets orbiting spotted stars, allowing the host star to be a source of contaminating positive or negative flux which influences the transit depths but not the ingress/egress durations. We find that none of the planets show statistically significant evidence for self-contamination by bright or dark regions of the stellar photosphere. However, we show that small-scale magnetic activity, analogous in size to the smallest sunspots, could still be lurking in the transit photometry undetected.

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https://arxiv.org/abs/1806.10084

Updated Compositional Models of the TRAPPIST-1 Planets

Cayman T. Unterborn, Natalie R. Hinkel, Steven J. Desch
(Submitted on 26 Jun 2018)

After publication of our initial mass-radius-composition models for the TRAPPIST-1 system in Unterborn et al. (2018), the planet masses were updated in Grimm et al. (2018). We had originally adopted the data set of Wang et al., 2017 who reported different densities than the updated values. The differences in observed density change the inferred volatile content of the planets. Grimm et al. (2018) report TRAPPIST-1 b, d, f, g, and h as being consistent with <5 wt% water and TRAPPIST-1 c and e has having largely rocky interiors. Here, we present updated results recalculating water fractions and potential alternative compositions using the Grimm et al., 2018 masses. Overall, we can only reproduce the results of Grimm et al., 2018 of planets b, d and g having small water contents if the cores of these planets are small (<23 wt%). We show that, if the cores for these planets are roughly Earth-sized (33 wt%), significant water fractions up to 40 wt% are possible. We show planets c, e, f, and h can have volatile envelopes between 0-35 wt% that are also consistent with being totally oxidized and lacking an Fe-core entirely. We note here that a pure MgSiO 3 planet (Fe/Mg = 0) is not the true lowest density end-member mass-radius curve for determining the probability of a planet containing volatiles. All planets that are rocky likely contain some Fe, either within the core or oxidized in the mantle. We argue the true low density end-member for oxidizing systems is instead a planet with the lowest reasonable Fe/Mg and completely core-less. Using this logic, we assert that planets b, d and g likely must have significant volatile layers because the end-member planet models produce masses too high even when uncertainties in both mass and radius are taken into account.

[Roger E. Moore]

A few more recent articles of importance....


https://arxiv.org/abs/1802.08300

Dimensionality and integrals of motion of the Trappist-1 planetary system

Johannes Floß, Hanno Rein, Paul Brumer
(Submitted on 22 Feb 2018 (v1), last revised 18 Apr 2018 (this version, v2))

The number of isolating integrals of motion of the Trappist-1 system - a late M-dwarf orbited by seven Earth-sized planets - was determined numerically, using an adapted version of the correlation dimension method. It was found that over the investigated time-scales of up to 20 000 years the number of isolating integrals of motion is the same as one would find for a system of seven non-interacting planets - despite the fact that the planets in the Trappist-1 system are strongly interacting. Considering perturbed versions of the Trappist-1 system shows that the system may occupy an atypical part of phase-space with high stability. These findings are consistent with earlier studies.

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https://arxiv.org/abs/1807.00378

The Impact of Stellar Distances on Habitable Zone Planets

Stephen R. Kane
(Submitted on 1 Jul 2018 (v1), last revised 11 Jul 2018 (this version, v2))

Among the most highly valued of exoplanetary discoveries are those of terrestrial planets found to reside within the Habitable Zone (HZ) of the host star. In particular, those HZ planets with relatively bright host stars will serve as priority targets for characterization observations, such as those involving mass determinations, transmission spectroscopy, and direct imaging. The properties of the star are greatly affected by the distance measurement to the star, and subsequent changes to the luminosity result in revisions to the extent of the HZ and the properties of the planet. This is particularly relevant in the realm of Gaia which has released updated stellar parallaxes for the known exoplanet host stars. Here we provide a generalized formulation of the effect of distance on planetary system properties, including the HZ. We apply this methodology to three known systems and show that the recent Gaia Data Release 2 distances have a modest effect for TRAPPIST-1 but a relatively severe effect for Kepler-186 and LHS 1140.

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https://link.springer.com/article/10...63772918060033

Activity of the M8 Dwarf TRAPPIST-1

Dmitrienko, E. S.; Savanov, I. S.
06/2018

The results of an analysis of observations of the cool (M8) dwarf TRAPPIST-1 obtained on the Kepler Space Telescope (the K2 continuation mission) are presented. TRAPPIST-1 possesses a planetary system containing at least seven planets. In all, the observations consist of 105 584 individual brightness measurements made over a total duration of 79 days. Brightness power spectra computed for TRAPPIST-1 exhibit a peak corresponding to P 0 = 3.296 ± 0.007 d . There are also two peaks with lower significances at P 1 = 2.908 d and P 2 = 2.869 d , which cannot be explained by the presence of differential rotation. The observational material available for TRAPPIST-1 is subdivided into 21 datasets, each covering one stellar rotation period. Each of the individual light curves was used to construct a map of the star's temperature inhomogeneities. On average, the total spotted area of TRAPPIST-1 was S = 5% of the entire visible area. The difference between the angular rotation rates at the equator and at the pole is estimated to be DeltaOmega = 0.006. The new results obtained together with data from the literature are used to investigate the properties of this unique star and compare them to the properties of other cool dwarfs. Special attention is paid to the star's evolutionary status (its age). All age estimates for TRAPPIST-1 based on its activity characteristics (rotation, spot coverage, UV and X-ray flux, etc.) indicate that the star is young.

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http://iopscience.iop.org/article/10...357/aac104/pdf

The Productivity of Oxygenic Photosynthesis around Cool, M Dwarf Stars

Lehmer, Owen R.; Catling, David C.; Parenteau, Mary N.; Hoehler, Tori M.
06/2018

In the search for life around cool stars, the presence of atmospheric oxygen is a prominent biosignature, as it may indicate oxygenic photosynthesis (OP) on the planetary surface. On Earth, most oxygenic photosynthesizing organisms (OPOs) use photons between 400 and 750 nm, which have sufficient energy to drive the photosynthetic reaction that generates O2 from H2O and CO2. OPOs around cool stars may evolve similar biological machinery capable of producing oxygen from water. However, in the habitable zones (HZs) of the coolest M dwarf stars, the flux of 400-750 nm photons may be just a few percent that of Earth's. We show that the reduced flux of 400-750 nm photons around M dwarf stars could result in Earth-like planets being growth limited by light, unlike the terrestrial biosphere, which is limited by nutrient availability. We consider stars with photospheric temperatures between 2300 and 4200 K and show that such light-limited worlds could occur at the outer edge of the HZ around TRAPPIST-1-like stars. We find that even if OP can use photons longer than 750 nm, there would still be insufficient energy to sustain the Earth's extant biosphere throughout the HZ of the coolest stars. This is because such stars emit largely in the infrared and near-infrared, which provide sufficient energy to make the planet habitable, but limits the energy available for OP. TRAPPIST-1f and g may fall into this category. Biospheres on such planets, potentially limited by photon availability, may generate small biogenic signals, which could be difficult for future observations to detect.

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http://iopscience.iop.org/article/10...881/aabee8/pdf

Dynamical Constraints on Nontransiting Planets Orbiting TRAPPIST-1

Jontof-Hutter, Daniel; Truong, Vinh H.; Ford, Eric B.; Robertson, Paul; Terrien, Ryan C.
06/2018

We derive lower bounds on the orbital distance and inclination of a putative planet beyond the transiting seven planets of TRAPPIST-1, for a range of masses ranging from 0.08 M Jup to 3.5 M Jup. While the outer architecture of this system will ultimately be constrained by radial velocity measurements over time, we present dynamical constraints from the remarkably coplanar configuration of the seven transiting planets, which is sensitive to modestly inclined perturbers. We find that the observed configuration is unlikely if a Jovian-mass planet inclined by >=3° to the transiting planet exists within 0.53 au, exceeding any constraints from transit timing variations (TTV) induced in the known planets from an undetected perturber. Our results will inform RV programs targeting TRAPPIST-1, and for near coplanar outer planets, tighter constraints are anticipated for radial velocity (RV) precisions of ≲140 m s-1. At higher inclinations, putative planets are ruled out to greater orbital distances with orbital periods up to a few years.

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https://arxiv.org/abs/1802.01377

The nature of the TRAPPIST-1 exoplanets

Simon L. Grimm, Brice-Olivier Demory, Michaël Gillon, Caroline Dorn, Eric Agol, Artem Burdanov, Laetitia Delrez, Marko Sestovic, Amaury H.M.J. Triaud, Martin Turbet, Émeline Bolmont, Anthony Caldas, Julien de Wit, Emmanuël Jehin, Jérémy Leconte, Sean N. Raymond, Valérie Van Grootel, Adam J. Burgasser, Sean Carey, Daniel Fabrycky, Kevin Heng, David M. Hernandez, James G. Ingalls, Susan Lederer, Franck Selsis, Didier Queloz
(Submitted on 5 Feb 2018)

The TRAPPIST-1 system hosts seven Earth-sized, temperate exoplanets orbiting an ultra-cool dwarf star. As such, it represents a remarkable setting to study the formation and evolution of terrestrial planets that formed in the same protoplanetary disk. While the sizes of the TRAPPIST-1 planets are all known to better than 5% precision, their densities have significant uncertainties (between 28% and 95%) because of poor constraints on the planet's masses. Aims.The goal of this paper is to improve our knowledge of the TRAPPIST-1 planetary masses and densities using transit-timing variations (TTV). The complexity of the TTV inversion problem is known to be particularly acute in multi-planetary systems (convergence issues, degeneracies and size of the parameter space), especially for resonant chain systems such as TRAPPIST-1. Methods. To overcome these challenges, we have used a novel method that employs a genetic algorithm coupled to a full N-body integrator that we applied to a set of 284 individual transit timings. This approach enables us to efficiently explore the parameter space and to derive reliable masses and densities from TTVs for all seven planets. Our new masses result in a five- to eight-fold improvement on the planetary density uncertainties, with precisions ranging from 5% to 12%. These updated values provide new insights into the bulk structure of the TRAPPIST-1 planets. We find that TRAPPIST-1c and -1e likely have largely rocky interiors, while planets b, d, f, g, and h require envelopes of volatiles in the form of thick atmospheres, oceans, or ice, in most cases with water mass fractions less than 5%.

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https://arxiv.org/abs/1804.10618

TRAPPIST-1e Has a Large Iron Core

Gabrielle Suissa, David Kipping
(Submitted on 26 Apr 2018)

The TRAPPIST-1 system provides an exquisite laboratory for understanding exoplanetary atmospheres and interiors. Their mutual gravitational interactions leads to transit timing variations, from which Grimm et al. (2018) recently measured the planetary masses with precisions ranging from 5% to 12%. Using these masses and the <5% radius measurements on each planet, we apply the method described in Suissa et al. (2018) to infer the minimum and maximum CRF (core radius fraction) of each planet. Further, we modify the maximum limit to account for the fact that a light volatile envelope is excluded for planets b through f. Only planet e is found to have a significant probability of having a non-zero minimum CRF, with a 0.7% false-alarm probability it has no core. Our method further allows us to measure the CRF of planet e to be greater than (49 +/- 7)% but less than (72 +/- 2)%, which is compatible with that of the Earth. TRAPPIST-1e therefore possess a large iron core similar to the Earth, in addition to being Earth-sized and located in the temperature zone.

[Roger E. Moore]

https://arxiv.org/abs/1712.05641

Interior Structures and Tidal Heating in the TRAPPIST-1 Planets

Amy C. Barr, Vera Dobos, László L. Kiss
(Submitted on 15 Dec 2017 (v1), last revised 24 Jan 2018 (this version, v2))

With seven planets, the TRAPPIST-1 system has the largest number of exoplanets discovered in a single system so far. The system is of astrobiological interest, because three of its planets orbit in the habitable zone of the ultracool M dwarf. Assuming the planets are composed of non-compressible iron, rock, and H 2 O, we determine possible interior structures for each planet. To determine how much tidal heat may be dissipated within each planet, we construct a tidal heat generation model using a single uniform viscosity and rigidity for each planet based on the planet's composition. With the exception of TRAPPIST-1c, all seven of the planets have densities low enough to indicate the presence of significant H 2 O in some form. Planets b and c experience enough heating from planetary tides to maintain magma oceans in their rock mantles; planet c may have eruptions of silicate magma on its surface, which may be detectable with next-generation instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are still twenty times higher than Earth's mean heat flow. Planets d and e are the most likely to be habitable. Planet d avoids the runaway greenhouse state if its albedo is ≳ 0.3. Determining the planet's masses within ∼0.1 to 0.5 Earth masses would confirm or rule out the presence of H 2 O and/or iron in each planet, and permit detailed models of heat production and transport in each planet. Understanding the geodynamics of ice-rich planets f, g, and h requires more sophisticated modeling that can self-consistently balance heat production and transport in both rock and ice layers.

[Roger E. Moore]

A very nice, large image of the TRAPPIST-1 planets, as NASA envisions them. The caption with the image is:

This chart shows, on the top row, artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii, masses, densities and surface gravity as compared to those of Earth.
Image credit: NASA/JPL-Caltech.

[BigDon]

Wow.

If this was a science fiction story I would smile and nod politely and hope the author didn't go into any more high fantasy...

[Roger E. Moore]

If this was a science fiction story I would smile and nod politely and hope the author didn't go into any more high fantasy...

In the old days (1970 or so), I would have labeled this as baloney and thrown out the book, because of course it was baloney to have seven Earths stacked on top of each other, etc. I mean, seriously.

[Roger E. Moore]

https://arxiv.org/abs/1802.02086

The Near-Infrared Transmission Spectra of TRAPPIST-1 Planets b, c, d, e, f, and g and Stellar Contamination in Multi-Epoch Transit Spectra

Zhanbo Zhang, Yifan Zhou, Benjamin V. Rackham, Daniel Apai
(Submitted on 6 Feb 2018 (v1), last revised 31 Aug 2018 (this version, v3))

The seven approximately Earth-sized transiting planets in the \object{TRAPPIST-1} system provide a unique opportunity to explore habitable zone and non-habitable zone small planets within the same system. Its habitable zone exoplanets -- due to their favorable transit depths -- are also worlds for which atmospheric transmission spectroscopy is within reach with the Hubble Space Telescope (HST) and with the James Webb Space Telescope (JWST). We present here an independent reduction and analysis of two \textit{HST} Wide Field Camera 3 (WFC3) near-infrared transit spectroscopy datasets for six planets (b through g). Utilizing our physically-motivated detector charge trap correction and a custom cosmic ray correction routine, we confirm the general shape of the transmission spectra presented by \textbf{\citet{deWit2016, deWit2018}}. Our data reduction approach leads to a 25\% increase in the usable data and reduces the risk of confusing astrophysical brightness variations (e.g., flares) with instrumental systematics. No prominent absorption features are detected in any individual planet's transmission spectra; by contrast, the combined spectrum of the planets shows a suggestive decrease around 1.4\,$\micron$ similar to an inverted water absorption feature. Including transit depths from \textit{K2}, the SPECULOOS-South Observatory, and \textit{Spitzer}, we find that the complete transmission spectrum is fully consistent with stellar contamination owing to the transit light source effect. These spectra demonstrate how stellar contamination can overwhelm planetary absorption features in low-resolution exoplanet transit spectra obtained by \textit{HST} and \textit{JWST} and also highlight the challenges in combining multi epoch observations for planets around rapidly rotating spotted stars.

[Roger E. Moore]

https://arxiv.org/abs/1807.01402

The 0.8-4.5μ m broadband transmission spectra of TRAPPIST-1 planets

E. Ducrot, et al.
(Submitted on 3 Jul 2018 (v1), last revised 2 Sep 2018 (this version, v2))

The TRAPPIST-1 planetary system represents an exceptional opportunity for the atmospheric characterization of temperate terrestrial exoplanets with the upcoming James Webb Space Telescope (JWST). Assessing the potential impact of stellar contamination on the planets' transit transmission spectra is an essential precursor step to this characterization. Planetary transits themselves can be used to scan the stellar photosphere and to constrain its heterogeneity through transit depth variations in time and wavelength. In this context, we present our analysis of 169 transits observed in the optical from space with K2 and from the ground with the SPECULOOS and Liverpool telescopes. Combining our measured transit depths with literature results gathered in the mid/near-IR with Spitzer/IRAC and HST/WFC3, we construct the broadband transmission spectra of the TRAPPIST-1 planets over the 0.8-4.5 μ m spectral range. While planets b, d, and f spectra show some structures at the 200-300ppm level, the four others are globally flat. Even if we cannot discard their instrumental origins, two scenarios seem to be favored by the data: a stellar photosphere dominated by a few high-latitude giant (cold) spots, or, alternatively, by a few small and hot (3500-4000K) faculae. In both cases, the stellar contamination of the transit transmission spectra is expected to be less dramatic than predicted in recent papers. Nevertheless, based on our results, stellar contamination can still be of comparable or greater order than planetary atmospheric signals at certain wavelengths. Understanding and correcting the effects of stellar heterogeneity therefore appears essential to prepare the exploration of TRAPPIST-1's with JWST.

[ngc3314]

In the old days (1970 or so), I would have labeled this as baloney and thrown out the book, because of course it was baloney to have seven Earths stacked on top of each other, etc. I mean, seriously.

I was deeply struck with this while setting up an outreach event using ping-pong balls to show the TRAPPIST-1 planets to scale with their orbits. They would be really obviously big to our unaided eyes. Running some numbers, from the innermost of the 7, the outermost and smallest would still show a distinct visible disk at opposition (about 4.5 arcminutes in diameter). It would look like some of the old magazine paintings of a downright crowded sky.

[Roger E. Moore]

Most recent paper is not optimistic about colonization conditions on any of the planets. If the temperature is okay, there's no water, there's sulfuric acid in the air, etc. Nonetheless, this is only a collection of simulations and maybe we'll find one of the seven suitable for building suburbs. Don't take your spacesuit off, though. Could be a terraformer's paradise.


https://arxiv.org/abs/1809.07498

Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System

Andrew P. Lincowski, et al. (Submitted on 20 Sep 2018)

The TRAPPIST-1 planetary system provides an unprecedented opportunity to study terrestrial exoplanet evolution with the James Webb Space Telescope (JWST) and ground-based observatories. Since M dwarf planets likely experience extreme volatile loss, the TRAPPIST-1 planets may have highly-evolved, possibly uninhabitable atmospheres. We used a versatile, 1D terrestrial-planet climate model with line-by-line radiative transfer and mixing length convection (VPL Climate) coupled to a terrestrial photochemistry model to simulate environmental states for the TRAPPIST-1 planets. We present equilibrium climates with self-consistent atmospheric compositions, and observational discriminants of post-runaway, desiccated, 10-100 bar O2- and CO2-dominated atmospheres, including interior outgassing, as well as for water-rich compositions. Our simulations show a range of surface temperatures, most of which are not habitable, although an aqua-planet TRAPPIST-1 e could maintain a temperate surface given Earth-like geological outgassing and CO2. We find that a desiccated TRAPPIST-1 h may produce habitable surface temperatures beyond the maximum greenhouse distance. Potential observational discriminants for these atmospheres in transmission and emission spectra are influenced by photochemical processes and aerosol formation, and include collision-induced oxygen absorption (O2-O2), and O3, CO, SO2, H2O, and CH4 absorption features, with transit signals of up to 200 ppm. Our simulated transmission spectra are consistent with K2, HST, and Spitzer observations of the TRAPPIST-1 planets. For several terrestrial atmospheric compositions, we find that TRAPPIST-1 b is unlikely to produce aerosols. These results can inform JWST observation planning and data interpretation for the TRAPPIST-1 system and other M dwarf terrestrial planets.

QUOTES: We have calculated the possible ocean loss and oxygen accumulation for the seven known TRAPPIST-1 planets, modeled potential O2/CO2-dominated and potentially habitable environments, and computed transit transmission and emission spectra. These evolved terrestrial exoplanet spectra are consistent with broad constraints from recent HST and Spitzer data. Our evolutionary modeling suggests that the current environmental states can include the hypothesized desiccated, post-ocean-runaway O2-dominated planets, with at least partial ocean loss persisting out to TRAPPIST-1 h. These O2 dominated atmospheres have unusual temperature structures, with low-altitude stratospheres and no tropospheres, which result in distinctive features in both transmission and emission, including strong collision-induced absorption from O2. Alternatively, if early volatile outgassing (e.g. H2O, SO2, CO2) occurred, as was the case for Earth and Venus, Venus-like atmospheres are possible, and likely stable, throughout and beyond the habitable zone, so the maximum greenhouse limit may not apply for evolved M dwarf planets. If Venus-like, these planets could form sulfuric acid hazes, though we find that TRAPPIST-1 b would be too hot to condense H2SO4 aerosols. From analyzing our simulated spectra, we find that there are observational discriminants for the environments we modeled in both transit and emission, with transit signals up to 200 ppm for TRAPPIST-1 b. Detection of CO2 in all considered compositions may be used to probe for the presence of a terrestrial atmosphere. We find that the detection of water is not a good indicator of a habitable environment, as Venus-like atmospheres exhibit similar spectral features for water, so the detection of low stratospheric water abundance maybe a necessary but not sufficient condition for a habitable environment. The discriminants between these environments involve several trace gases. Careful atmospheric modeling that includes photochemistry and realistic interior out gassing is required to predict the diversity of potentially observable spectral features, to interpret future data, and to infer the underlying physical processes producing the observed features. Nevertheless, these discriminants may be used to assess the viability of detecting evolutionary outcomes for the TRAPPIST-1 planets with upcoming observatories, particularly JWST, and this will be assessed in subsequent work. While specifically applied here to the TRAPPIST-1 system, our results may be broadly relevant for other multi-planet M dwarf systems.

[Roger E. Moore]

TRAPPIST-1's LAW: If it is at all possible for the TRAPPIST-1 system to get any more complicated than it already is, that possibility will immediately reach 100% and a paper will come out to prove it.


https://arxiv.org/abs/1809.08166

Planet-Planet Tides in the TRAPPIST-1 System

Jason T. Wright (Submitted on 21 Sep 2018)

The star TRAPPIST-1 hosts a system of seven transiting, terrestrial exoplanets apparently in a resonant chain, at least some of which are in or near the Habitable Zone. Many have examined the roles of tides in this system, as tidal dissipation of the orbital energy of the planets may be relevant to both the rotational and orbital dynamics of the planets, as well as their habitability. Generally, tides are calculated as being due to the tides raised on the planets by the star, and tides raised on the star by the planets. I write this research note to point out a tidal effect that may be at least as important as the others in the TRAPPIST-1 system and which is so far unremarked upon in the literature: planet-planet tides. Under some reasonable assumptions, I find that for every planet p in the TRAPPIST-1 system there exists some other planet q for which the planet-planet dynamical tidal strain is within an order of magnitude of the stellar eccentricity tidal strain, and that the effects of planet f on planet g are in fact greater than that of the star on planet g. It is thus not obvious that planet-planet tides can be neglected in the TRAPPIST-1 exoplanetary system, especially the tides on planet g due to planet f, if the planets are in synchronous rotation.

[Roger E. Moore]

I note that "Planet-Planet Tides in the TRAPPIST-1 System" has just been updated. If you are interested in this paper you might wish to recheck it to see if anything else has changed.

[Roger E. Moore]

Can you see the stars from the TRAPPIST-1 planets? Maybe not.


https://arxiv.org/abs/1810.05210

Limits on Clouds and Hazes for the TRAPPIST-1 Planets

Sarah E. Moran, et al. (Submitted on 11 Oct 2018)

The TRAPPIST-1 planetary system is an excellent candidate for study of the evolution and habitability of M-dwarf planets. Transmission spectroscopy observations performed with the Hubble Space Telescope (HST) suggest the innermost five planets do not possess clear hydrogen atmospheres. Here we reassess these conclusions with recently updated mass constraints and expand the analysis to include limits on metallicity, cloud top pressure, and the strength of haze scattering. We connect recent laboratory results of particle size and production rate for exoplanet hazes to a one-dimensional atmospheric model for TRAPPIST-1 transmission spectra. Doing so, we obtain a physically-based estimate of haze scattering cross sections. We find haze scattering cross sections on the order of 1e-26 to 1e-19 cm squared are needed in hydrogen-rich atmospheres for TRAPPIST-1 d, e, and f to match the HST data. For TRAPPIST-1 g, we cannot rule out a clear hydrogen-rich atmosphere. We also modeled the effects an opaque cloud deck and substantial heavy element content have on the transmission spectra. We determine that hydrogen-rich atmospheres with high altitude clouds, at pressures of 12mbar and lower, are consistent with the HST observations for TRAPPIST-1 d and e. For TRAPPIST-1 f and g, we cannot rule out clear hydrogen-rich cases to high confidence. We demonstrate that metallicities of at least 60xsolar with tropospheric (0.1 bar) clouds agree with observations. Additionally, we provide estimates of the precision necessary for future observations to disentangle degeneracies in cloud top pressure and metallicity. Our results suggest secondary, volatile-rich atmospheres for the outer TRAPPIST-1 planets d, e, and f.

[Roger E. Moore]

One thing not greatly explored for TRAPPIST-1's planets is whether they generate earth tides on each other, and therefore a lot of internal heat and volcanism, as happens on Io.

https://arxiv.org/abs/1810.11255

Constraining the environment and habitability of TRAPPIST-1

Emeline Bolmont (Submitted on 26 Oct 2018)

The planetary system of TRAPPIST-1, discovered in 2016-2017, is a treasure-trove of information. Thanks to a combination of observational techniques, we have estimates of the radii and masses of the seven planets of this very exotic system. With three planets within the traditional Habitable Zone limits, it is one of the best constrained system of astrobiological interest. I will review here the theoretical constraints we can put on this system by trying to reconstruct its history: its atmospheric evolution which depends on the luminosity evolution of the dwarf star, and its tidal dynamical evolution. These constraints can then be used as hypotheses to assess the habitability of the outer planets of the system with a Global Climate Model.

QUOTES: In many aspects, TRAPPIST-1 is comparable to the system of Jupiter and its satellites. The eccentricity of Io is damped by tides and excited by the other satellites (especially by Europa and Ganymede, in mean motion resonance with Io), this leads to a small remnant equilibrium eccentricity of ~ 0.004. This non-zero eccentricity leads to a tidal deformation of the satellite, which is responsible for the observed intense surface activity (tidal heat flux of ~ 3 W/m2, Spencer et al. 2000; intense volcanic activity, Spencer et al. 2007). The exact same situation is true for the planets of TRAPPIST-1. The tidal heat flux for each planets has been evaluated in Luger et al. (2017) and Turbet et al. (2018). In particular the flux of TRAPPIST-1b is always higher than Io's and the flux of planets c and d are higher than the heat flux of Earth (Pollack et al. 1993; Davies & Davies 2010). Depending on the assumption on the dissipation of the planets, TRAPPIST-1e can experience a tidal heat flux of the order of magnitude of Earth's heat flux. The effect of this tidal heat flux on the internal structure of the planets (Barr et al. 2018) and their climate (Turbet et al. 2018) should be investigated further (see Sylvain Breton's proceeding from this same conference).

[Roger E. Moore]

Cannot get the original research paper, but there's this news bit on Panspermia within TRAPPIST-1.


https://phys.org/news/2018-10-life-planets-door.html

Sharing life with the planets next door
October 30, 2018 by Starre Vartan, Astrobiology Magazine

Dr. Dimitri Veras, an astrophysicist at the University of Warwick in the UK, and lead author of a new paper on the subject, says that, "Within the last century, [panspermia] has been focused on life transport within the solar system, including Earth." The TRAPPIST-1 system, which is 41 light years away and includes seven planets packed into an orbit smaller than Mercury's, changes this Earth-centric idea. The TRAPPIST-1 sun is an ultra-cool red dwarf, so even though the seven nearby planets orbit closely, they are possibly all still in the habitable zone for life, to varying degrees depending upon the make-up of their atmospheres. That makes them a perfect model for exploring the idea of panspermia, per Hawking, anywhere in the universe.

[Roger E. Moore]

Continuing to try to keep up with the TRAPPIST-1 family, looking at stellar flares' effects on the planets, and whether the star is messing up atmospheric evaluations of one of the worlds.


https://arxiv.org/abs/1811.04149

Magnetic Fields on the Flare Star Trappist-1: Consequences for Radius Inflation and Planetary Habitability

D. J. Mullan, J. MacDonald, S. Dieterich, H. Fausey (Submitted on 9 Nov 2018)

We construct evolutionary models of Trappist-1 in which magnetic fields impede the onset of convection according to a physics-based criterion. In the models that best fit all observational constraints, the photospheric fields in Tr-1 are found to be in the range 1450-1700 G. These are weaker by a factor of about 2 than the fields we obtained in previous magnetic models of two other cool dwarfs (GJ65A/B). Our results suggest that Tr-1 possesses a global poloidal field which is some one hundred times stronger than in the Sun. In the context of exoplanets in orbit around Tr-1, the strong poloidal fields on the star may help to protect the planets from the potentially destructive effects of coronal mass ejections. This, in combination with previous arguments about beneficial effects of flare photons in ultraviolet and visible portions of the spectrum, suggests that conditions on Tr-1 are not necessarily harmful to life on a planet in the habitable zone of Tr-1.

========

https://arxiv.org/abs/1811.04877

Disentangling the planet from the star in late type M dwarfs: A case study of TRAPPIST-1g

Hannah R. Wakeford, et al. (Submitted on 12 Nov 2018)

The atmospheres of late M stars represent a significant challenge in the characterization of any transiting exoplanets due to the presence of strong molecular features in the stellar atmosphere. TRAPPIST-1 is an ultra-cool dwarf, host to seven transiting planets, and contains its own molecular signatures which can potentially be imprinted on planetary transit light curves due to inhomogeneities in the occulted stellar photosphere. We present a case study on TRAPPIST-1g, the largest planet in the system, using a new observation together with previous data, to disentangle the atmospheric transmission of the planet from that of the star. We use the out-of-transit stellar spectra to reconstruct the stellar flux based on one-, two-, and three-temperature components. We find that TRAPPIST-1 is a 0.08 M∗, 0.117 R∗, M8V star with a photospheric effective temperature of 2400 K, with ~35% 3000 K spot coverage and a very small fraction, <3%, of ~5800 K hot spot. We calculate a planetary radius for TRAPPIST-1g to be Rp = 1.124 R⊕ with a planetary density of ρp = 0.8214 ρ⊕. Based on the stellar reconstruction there are eleven plausible scenarios for the combined stellar photosphere and planet transit geometry; in our analysis we are able to rule out 8 of the 11 scenarios. Using planetary models we evaluate the remaining scenarios with respect to the transmission spectrum of TRAPPIST-1g. We conclude that the planetary transmission spectrum is likely not contaminated by any stellar spectral features, and are able to rule out a clear solar H2/He-dominated atmosphere at greater than 3-sigma.

[Roger E. Moore]

New climate model renders all but one TRAPPIST-1 planet a dud.


https://phys.org/news/2018-11-climat...ntriguing.html

Study brings new climate models of small star TRAPPIST 1's seven intriguing worlds
November 21, 2018 by Peter Kelley, University of Washington

Not all stars are like the sun, so not all planetary systems can be studied with the same expectations. New research from a University of Washington-led team of astronomers gives updated climate models for the seven planets around the star TRAPPIST-1. The work also could help astronomers more effectively study planets around stars unlike our sun, and better use the limited, expensive resources of the James Webb Space Telescope, now expected to launch in 2021.

"We are modeling unfamiliar atmospheres, not just assuming that the things we see in the solar system will look the same way around another star," said Andrew Lincowski, UW doctoral student and lead author of a paper published Nov. 1 in Astrophysical Journal. "We conducted this research to show what these different types of atmospheres could look like." The team found, briefly put, that due to an extremely hot, bright early stellar phase, all seven of the star's worlds may have evolved like Venus, with any early oceans they may have had evaporating and leaving dense, uninhabitable atmospheres. However, one planet, TRAPPIST-1 e, could be an Earthlike ocean world worth further study, as previous research also has indicated.

TRAPPIST-1, 39 light-years or about 235 trillion miles away, is about as small as a star can be and still be a star. A relatively cool "M dwarf" star—the most common type in the universe—it has about 9 percent the mass of the sun and about 12 percent its radius. TRAPPIST-1 has a radius only a little bigger than the planet Jupiter, though it is much greater in mass.

Actual paper
https://arxiv.org/abs/1809.07498

[Roger E. Moore]

This recent study indicates that the low-mass star (M8) TRAPPIST-1 has condensates in its upper atmosphere... i.e., "clouds".


https://arxiv.org/abs/1901.02041

Time-resolved image polarimetry of Trappist-1 during planetary transits

P. A. Miles-Páez, M. R. Zapatero Osorio, E. Pallé, S. A. Metchev (Submitted on 7 Jan 2019)

We obtained linear polarization photometry (J -band) and low-resolution spectroscopy (ZJ -bands) of Trappist-1, which is a planetary system formed by an M8-type low-mass star and seven temperate, Earth-sized planets. The photopolarimetric monitoring campaign covered 6.5 h of continuous observations including one full transit of planet Trappist-1d and partial transits of Trappist-1b and e. The spectrophotometric data and the photometric light curve obtained over epochs with no planetary transits indicate that the low-mass star has very low level of linear polarization compatible with a null value. However, the "in transit" observations reveal an enhanced linear polarization signal with peak values of p ∗ =0.1% with a confidence level of 3 σ , particularly for the full transit of Trappist-1d, thus confirming that the atmosphere of the M8-type star is very likely dusty. Additional observations probing different atmospheric states of Trappist-1 are needed to confirm our findings, as the polarimetric signals involved are low. If confirmed, polarization observations of transiting planetary systems with central ultra-cool dwarfs can become a powerful tool for the characterization of the atmospheres of the host dwarfs and the validation of transiting planet candidates that cannot be corroborated by any other method.

QUOTES: Trappist-1 has an effective temperature T-eff = 2516 +/- 41 K (Van Grootel et al. 2018); this is low enough for naturally forming liquid and solid condensates in the upper photosphere... These condensates [are] sometimes referred to as "dusty" particles that can be organized into "clouds"

[Roger E. Moore]

It is possible that the innermost worlds of TRAPPIST-1 interact with their sun as to produce stellar flares.


https://arxiv.org/abs/1901.02747

Time-variable electromagnetic star-planet interaction: The TRAPPIST-1 system as an exemplary case

Christian Fischer, Joachim Saur (Submitted on 9 Jan 2019)

Exoplanets sufficiently close to their host star can in principle couple electrodynamically to the star. This process is known as electrodynamic star-planet interaction (SPI). The expected emission associated with this coupling is however difficult to observe due to the bright intrinsic stellar emission. Identification of time-variability in the stellar lightcurve is one of the most promising approaches to identify SPI. In this work we therefore systematically investigate various mechanisms and their associated periods, which generate time-variability to aid the search for SPI. We find that the synodic and half the synodic rotation periods of the stars as measured in the rest frames of the orbiting exoplanets are basic periods occurring in SPI. We apply our findings to the example of TRAPPIST-1 with its seven close-in planets for which we investigate the possibility of SPI and the associated time-variabilities. We show that especially TRAPPIST-1b and c, are very likely subject to sub-Alfvénic interaction, a necessary condition for SPI. Both planets are therefore expected to generate Alfvén wings, which can couple to the star. The associated Poynting fluxes are on the order of 10 11 to 10 15 W and thus can hardly be the direct source of currently observable time-variability from TRAPPIST-1. However these Poynting fluxes might trigger flares on the star. We find correlations between the observed flares and the expected planetary induced signals, which could be due to SPI but our findings are not conclusive and warrant further observations and modelling.

QUOTES: We performed an analysis of TRAPPIST-1's are time-series as observed by the K2-mission (Luger et al. 2017). Our results hint at a quasi-periodic occurrence of flares with T1c's synodic period of 9.1 d and the stellar rotation period of 3.3 d but the results are inconclusive.

[Roger E. Moore]

Another look at stellar radiation bombardment of TRAPPIST-1 and similar planetary systems.

https://arxiv.org/abs/1902.03732

Stellar energetic particles in the magnetically turbulent habitable zones of TRAPPIST-1-like planetary systems

F. Fraschetti, J. J. Drake, J. D. Alvarado-Gomez, S. P. Moschou, C. Garraffo, O. Cohen (Submitted on 11 Feb 2019)

Planets in close proximity to their parent star, such as those in the habitable zones around M dwarfs, could be subject to particularly high doses of particle radiation. We have carried out test-particle simulations of ~GeV protons to investigate the propagation of energetic particles accelerated by flares or travelling shock waves within the stellar wind and magnetic field of a TRAPPIST-1-like system. Turbulence was simulated with small-scale magnetostatic perturbations with an isotropic power spectrum. We find that only a few percent of particles injected within half a stellar radius from the stellar surface escape, and that the escaping fraction increases strongly with increasing injection radius. Escaping particles are increasingly deflected and focused by the ambient spiralling magnetic field as the superimposed turbulence amplitude is increased. In our TRAPPIST-1-like simulations, regardless of the angular region of injection, particles are strongly focused onto two caps within the fast wind regions and centered on the equatorial planetary orbital plane. Based on a scaling relation between far-UV emission and energetic protons for solar flares applied to M dwarfs, the innermost putative habitable planet, TRAPPIST-1e, is bombarded by a proton flux up to 6 orders of magnitude larger than experienced by the present-day Earth. We note two mechanisms that could strongly limit EP fluxes from active stars: EPs from flares are contained by the stellar magnetic field; and potential CMEs that might generate EPs at larger distances also fail to escape.

===

Are the TRAPPIST-1 planets habitable from the standpoint of heat and runaway greenhouse effects?

https://arxiv.org/abs/1902.03867

Tidal Heating and the Habitability of the TRAPPIST-1 Exoplanets

Vera Dobos, Amy C. Barr, László L. Kiss (Submitted on 11 Feb 2019)

Context. New estimates of the masses and radii of the seven planets orbiting the ultracool M-dwarf TRAPPIST-1 star permit improved modelling of their compositions, heating by tidal dissipation, and removal of tidal heat by solid-state convection. Aims. Here, we compute the heat flux due to insolation and tidal heating for the inner four planets. Methods. We apply a Maxwell viscoelastic rheology to compute the tidal response of the planets using the volume-weighted average of the viscosities and rigidities of the metal, rock, high-pressure ice and liquid water/ice I layers. Results. We show that TRAPPIST-1d and e can avoid entering a runaway greenhouse state. Planet e is the most likely to support a habitable environment, with Earth-like surface temperatures and possibly liquid water oceans. Planet d also avoids a runaway greenhouse, if its surface reflectance is at least as high as that of the Earth. Planets b and c, closer to the star, have heat fluxes high enough to trigger a runaway greenhouse and support volcanism on the surfaces of their rock layers, rendering them too warm for life. Planets f, g, and h are too far from the star to experience significant tidal heating, and likely have solid ice surfaces with possible subsurface liquid water oceans.

[Roger E. Moore]

Imagine the tides if several planets line up at once. Bad day to go to the beach.

https://arxiv.org/abs/1903.04501

Tides between the TRAPPIST-1 planets

Hamish Hay, Isamu Matsuyama (Submitted on 11 Mar 2019)

The TRAPPIST-1 system is sufficiently closely packed that tides raised by one planet on another are significant. We investigate whether this source of tidal heating is comparable to eccentricity tides raised by the star.

[Roger E. Moore]

A bit dense, but fans of the TRAPPIST system might find value in this.

https://arxiv.org/abs/1905.00512

The tidal parameters of TRAPPIST-1 b and c

R. Brasser, A. C. Barr, V. Dobos (Submitted on 1 May 2019)

The TRAPPIST-1 planetary system consists of seven planets within 0.05 au of each other, five of which are in a multi-resonant chain. {These resonances suggest the system formed via planet migration; subsequent tidal evolution has damped away most of the initial eccentricities. We used dynamical N-body simulations to estimate how long it takes for the multi-resonant configuration that arises during planet formation to break. From there we use secular theory to pose limits on the tidal parameters of planets b and c. We calibrate our results against multi-layered interior models constructed to fit the masses and radii of the planets, from which the tidal parameters are computed independently.} The dynamical simulations show that the planets typically go unstable 30 Myr after their formation. {Assuming synchronous rotation throughout} we compute \frac{k_2}{Q} \gtrsim 2\times 10^{-4} for planet b and \frac{k_2}{Q} \gtrsim 10^{-3} for planet c. Interior models yield (0.075-0.37) \times 10^{-4} for TRAPPIST-1 b and (0.4-2)\times 10^{-4} for TRAPPIST-1 c. The agreement between the {dynamical and interior} models is not too strong, but is still useful to constrain the dynamical history of the system. We suggest that this two-pronged approach could be of further use in other multi-resonant systems if the planet's orbital and interior parameters are sufficiently well known.

[Roger E. Moore]

No further terrestrial or larger planets detected in the TRAPPIST-1 system. We seem to have found all the bigger ones.

https://arxiv.org/abs/1905.06035

Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared

A. Y. Burdanov, et al. (Submitted on 15 May 2019)

The TRAPPIST-1 planetary system is a favorable target for the atmospheric characterization of temperate earth-sized exoplanets by means of transmission spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible obstacle to this technique could come from the photospheric heterogeneity of the host star that could affect planetary signatures in the transit transmission spectra. To constrain further this possibility, we gathered an extensive photometric data set of 25 TRAPPIST-1 transits observed in the near-IR J band (1.2 μ m) with the UKIRT and the AAT, and in the NB2090 band (2.1 μ m) with the VLT during the period 2015-2018. In our analysis of these data, we used a special strategy aiming to ensure uniformity in our measurements and robustness in our conclusions. We reach a photometric precision of ∼0.003 (RMS of the residuals), and we detect no significant temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the period of three years. The few transit depths measured for planets d and f hint towards some level of variability, but more measurements will be required for confirmation. Our depth measurements for planets b and c disagree with the stellar contamination spectra originating from the possible existence of bright spots of temperature 4500 K. We report updated transmission spectra for the six inner planets of the system which are globally flat for planets b and g and some structures are seen for planets c, d, e, and f.

[Roger E. Moore]

Not a good discovery, if we are talking about the chances for life in the TRAPPIST-1 system.

https://arxiv.org/abs/1906.05250

On The XUV Luminosity Evolution of TRAPPIST-1

David P. Fleming, Rory Barnes, Rodrigo Luger, Jacob T. VanderPlas (Submitted on 12 Jun 2019)

We model the long-term XUV luminosity of TRAPPIST-1 to constrain the evolving high-energy radiation environment experienced by its planetary system. Using Markov Chain Monte Carlo (MCMC), we derive probabilistic constraints for TRAPPIST-1's stellar and XUV evolution that account for observational uncertainties, degeneracies between model parameters, and empirical data of low-mass stars. We constrain TRAPPIST-1's mass to m⋆ =0.089 ± 0.001 M⊙ and find that its early XUV luminosity likely saturated at log 10 (L XUV /L bol )= −3.05 +0.24 −0.10. From our posterior distributions, we infer that there is a ∼43% chance that TRAPPIST-1 is still in the saturated phase today, suggesting that TRAPPIST-1 has maintained high activity and L XUV /L bol ≈10 −3 for several Gyrs. TRAPPIST-1's planetary system therefore likely experienced a persistent and extreme XUV flux environment, potentially driving significant atmospheric erosion and volatile loss. The inner planets likely received XUV fluxes ∼10^3 − 10^4 × that of the modern Earth during TRAPPIST-1's 1 Gyr-long pre-main sequence phase. Deriving these constraints via MCMC is computationally non-trivial, so scaling our methods to constrain the XUV evolution of a larger number of M dwarfs that harbor terrestrial exoplanets would incur significant computational expenses. We demonstrate that approxposterior, a Python machine learning package for approximate Bayesian inference using Gaussian processes, can efficiently replicate our analysis. We find that it derives constraints that are in good agreement with our MCMC, although it underestimates the uncertainties for two parameters by 30% . approxposterior requires 330× less computational time than traditional MCMC methods in this case, demonstrating its utility in efficient Bayesian inference.

[Roger E. Moore]

No bad news for TRAPPIST-1 worlds' habitability.

https://arxiv.org/abs/1907.02112
Constraining the Radio Emission of TRAPPIST-1
Anna Hughes, Aaron Boley, Rachel Osten, Jacob White (Submitted on 3 Jul 2019)
Exposure to outgoing high energy particle radiation - traceable by radio flux - can erode planetary atmospheres. While our results do not imply that the TRAPPIST-1 planets are suitable for life, we find no evidence that they are overtly unsuitable due to proton fluxes.

[Roger E. Moore]

Where could the TRAPPIST-1 planets have gotten water? Is there a local equal to the Kuiper Belt there?

https://phys.org/news/2020-04-trappist-planets.html

[Roger E. Moore]

TRAPPIST-1 planets are not greatly misaligned with their star's plane of rotation, say Japanese researchers with Subaru telescope.

https://phys.org/news/2020-05-trappi...isaligned.html

[Roger E. Moore]

The seven rocky planets of TRAPPIST-1 seem to have very similar compositions. The red dwarf star TRAPPIST-1 is home to the largest group of roughly Earth-size planets ever found in a single stellar system. Located about 40 light-years away, these seven rocky siblings provide an example of the tremendous variety of planetary systems that likely fill the universe. A new study published today in the Planetary Science Journal shows that the TRAPPIST-1 planets have remarkably similar densities. That could mean they all contain about the same ratio of materials thought to compose most rocky planets, like iron, oxygen, magnesium, and silicon. But if this is the case, that ratio must be notably different than Earth's: The TRAPPIST-1 planets are about 8% less dense than they would be if they had the same makeup as our home planet. Based on that conclusion, the paper authors hypothesized a few different mixtures of ingredients could give the TRAPPIST-1 planets the measured density.

https://phys.org/news/2021-01-rocky-...positions.html