Modeling climate diversity, tidal dynamics and the fate of volatiles on TRAPPIST-1 planets

By M. Turbet, É. Bolmont, J. Leconte, Francois Forget, F. Selsis, Gabriel Tobie, Anthony Caldas, J. Naar, M. Gillon. 2017

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TRAPPIST-1 planets are invaluable for the study of comparative planetary science outside our Solar System and possibly habitability. First, we derive from N-body simulations possible planetary evolution scenarios, and show that each of the planets are likely to be in synchronous rotation. We then use a 3-D Global Climate Model to explore the possible climates of cool planets of the TRAPPIST-1 system. In particular, we look at the conditions required for cool planets to prevent possible volatile species to be lost by permanent condensation, irreversible burying or photochemical destruction. We also explore the resilience of the same volatiles (when in condensed phase) to a runaway greenhouse process. We find that background atmospheres made of N2, CO or O2 are resistant to atmospheric collapse. However, it should be difficult for TRAPPIST-1 planets to accumulate significant greenhouse gases like CO2, CH4, or NH3. CO2 can easily condense on the nightside, forming glaciers that would flow toward the substellar region. A complete CO2 ice cover is possible on TRAPPIST-1g and h only, although CO2 ice deposits could be gravitationally unstable and get buried beneath the water ice shell in geologically short timescales. Given TRAPPIST-1 planets large EUV irradiation (at least 1000x Titan's flux), CH4 and NH3 should be photodissociated rapidly and thus be hard to accumulate in the atmosphere. Photochemical hazes could then sedimentate and form a surface layer of tholins. Regarding habitability, we confirm that few bars of CO2 would suffice to warm the surface of TRAPPIST-1f and g above the melting point of water. We also show that TRAPPIST-1e is a remarkable candidate for surface habitability. If the planet is today synchronous and abundant in water, then it should always sustain surface liquid water at least in the substellar region, whatever the atmosphere considered.

Subfields: Astronomy and Astrophysics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/f521732e00fcf0413cc8e0479cfce096bfc1292e

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Citations in the corpus

Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST (2017, methodology): “…the complex atmospheric chemistry models that would be required to examine this in detail, but we discuss briefly how photochemistry could affect the compositions and spectra of some of these planets (see also Turbet et al. (2017) for more discussion of photodissociation in the TRAPPIST-1 planets).”
The nature of the TRAPPIST-1 exoplanets. (2018, methodology): “Calculations are performed using a synthetic spectrum of TRAPPIST-1 and molecular spectroscopic properties from Turbet et al. (2017).”
Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System (2018, methodology): “For the desiccated planets that we model here, we also assume dense ( 10 bar) atmospheres that will have smaller day–night contrast and are more likely to be stable against collapse (Hu & Yang 2014; Meadows et al. 2018a; Turbet et al. 2018).”