The Erosion Of Large Primary Atmospheres Typically Leaves Behind Substantial Secondary Atmospheres On Temperate Rocky Planets

Exoplanet exploration has revealed that many–perhaps most–terrestrial exoplanets formed with substantial H₂-rich envelopes, seemingly in contrast to solar system terrestrials, for which there is scant evidence of long-lived primary atmospheres. It is not known how a long-lived primary atmosphere might affect the subsequent habitability prospects of terrestrial exoplanets.

Here, we present a new, self-consistent evolutionary model of the transition from primary to secondary atmospheres. The model incorporates all Fe-C-O-H-bearing species and simulates magma ocean solidification, radiative-convective climate, thermal escape, and mantle redox evolution. For our illustrative example TRAPPIST-1, our model strongly favors atmosphere retention for the habitable zone planet TRAPPIST-1e.

In contrast, the same model predicts a comparatively thin atmosphere for the Venus-analog TRAPPIST-1b, which would be vulnerable to complete erosion via non-thermal escape and is consistent with JWST observations.

More broadly, we conclude that the erosion of primary atmospheres typically does not preclude surface habitability, and frequently results in large surface water inventories due to the reduction of FeO by H₂.

Monte Carlo evolutionary calculation showing outcomes for TRAPPIST 1e (left two columns) and TRAPPIST-1b (right two columns) after 8 Gyr of coupled atmosphere-interior-redox evolution, as a function of initial H endowment. Rows denote total surface pressure (bar), partial pressures of surface volatiles (bar), final atmosphere and interior carbon inventories (kg C), and final atmosphere and interior hydrogen inventories (kg H), respectively. The two columns for each planet denote endmember cases whereby all metallic iron is sequestered in the core (left), and all metallic iron remains in the silicate mantle (right). Solid lines and shaded regions denote median model outputs and 1-sigma confidence intervals, respectively. The green-shaded ranges denote approximate modern Bulk Silicate Earth (BSE) volatile abundances, and the red gradients show total surface volatile inventories increasingly vulnerable to non-thermal escape— final volatile inventories in the red-shaded region represent model runs that could result in airless planets. Broadly speaking, TRAPPIST-1e is expected to retain substantial volatiles and habitability is not precluded, whereas TRAPPIST-1b is likely to be left with a comparatively thin O₂ atmosphere susceptible to complete erosion via non-thermal loss. — astro-ph.EP

Joshua Krissansen-Totton, Nicholas Wogan, Maggie Thompson, Jonathan J. Fortney

Comments: Published in Nature Communications. 16 pages, 5 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2409.18940 [astro-ph.EP] (or arXiv:2409.18940v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2409.18940
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Journal reference: Nature Communications 15, 8374 (2024)
Related DOI:
https://doi.org/10.1038/s41467-024-52642-6
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Submission history
From: Joshua Krissansen-Totton
[v1] Fri, 27 Sep 2024 17:40:25 UTC (6,861 KB)
https://arxiv.org/abs/2409.18940

Astrobiology