TRAPPIST-1

Predictions For Observable Atmospheres Of Trappist-1 Planets From A Fully Coupled Atmosphere-Interior Evolution Model

By Keith Cowing
astro-ph.EP
July 11, 2022
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Predictions For Observable Atmospheres Of Trappist-1 Planets From A Fully Coupled Atmosphere-Interior Evolution Model
Schematic of PACMAN geochemical evolution model applied to Trappist-1 planets. The redox budget, thermal-climate evolution, and volatile budget are modeled from initial magma ocean (left) through to temperate geochemical cycling (right). Oxygen fluxes are shown by green arrows, energy fluxes by black arrows, carbon fluxes by orange arrows, and water fluxes by blue arrows; the net loss of hydrogen to space effectively adds oxygen to the atmosphere. During the magma ocean phase, the radius of solidification, rs, begins at the core–mantle boundary and moves toward the surface as internal heat is dissipated. The rate at which this occurs is controlled by radiogenic and tidal heat production, qinternal, convective heat flow from the mantle to the surface, qmantle, and heat flow from the core, Qcore. This internal heat flow balances the difference between outgoing longwave radiation (OLR), and incoming absorbed shortwave radiation (ASR). The oxygen fugacity of the mantle, fO2, and the water and carbon content mantle and surface reservoirs are tracked throughout. This schematic is an adapted and updated version from Krissansen-Totton et al. (2021b).

The Trappist-1 planets provide a unique opportunity to test the current understanding of rocky planet evolution.

The James Webb Space Telescope is expected to characterize the atmospheres of these planets, potentially detecting CO2, CO, H2O, CH4, or abiotic O2 from water photodissociation and subsequent hydrogen escape.

Here, we apply a coupled atmosphere-interior evolution model to the Trappist-1 planets to anticipate their modern atmospheres. This model, which has previously been validated for Earth and Venus, connects magma ocean crystallization to temperate geochemical cycling. Mantle convection, magmatic outgassing, atmospheric escape, crustal oxidation, a radiative-convective climate model, and deep volatile cycling are explicitly coupled to anticipate bulk atmospheres and planetary redox evolution over 8 Gyr. By adopting a Monte Carlo approach that samples a broad range of initial conditions and unknown parameters, we make some tentative predictions about current Trappist-1 atmospheres.

We find that anoxic atmospheres are probable, but not guaranteed, for the outer planets; oxygen produced via hydrogen loss during the pre-main sequence is typically consumed by crustal sinks. In contrast, oxygen accumulation on the inner planets occurs in around half of all models runs. Complete atmospheric erosion is possible but not assured for the inner planets (occurs in 20%-50% of model runs), whereas the outer planets retain significant surface volatiles in virtually all model simulations.

For all planets that retain substantial atmospheres, CO2-dominated or CO2-O2 atmospheres are expected; water vapor is unlikely to be a detectable atmospheric constituent in most cases. There are necessarily many caveats to these predictions, but the ways in which they misalign with upcoming observations will highlight gaps in terrestrial planet knowledge.

Joshua Krissansen-Totton, Jonathan J. Fortney

Comments: Main text 16 pages, 11 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2207.04164 [astro-ph.EP] (or arXiv:2207.04164v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2207.04164
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Journal reference: The Astrophysical Journal 2022, Volume 933, Number 1
Related DOI:
https://doi.org/10.3847/1538-4357/ac69cb
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Submission history
From: Joshua Krissansen-Totton
[v1] Sat, 9 Jul 2022 00:28:02 UTC (8,563 KB)
https://arxiv.org/abs/2207.04164
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