Redox Evolution via Gravitational Differentiation on Low Mass Planets: Implications for Biosignatures, Water Loss and Habitability

The oxidation of rocky planet surfaces and atmospheres, which arises from the twin forces of stellar nucleosynthesis and gravitational differentiation, is a universal process of key importance to habitability and exoplanet biosignature detection.

Here we develop a new generalized approach to this phenomenon. Using a single parameter to describe redox state, we model the coupled atmosphere-interior evolution of a range of terrestrial planets around nearby M stars and the Sun. Our model includes atmospheric photochemistry, diffusion and escape, line-by-line climate calculations and interior thermodynamics and chemistry. For many terrestrial planets, we find that abiotic O2 buildup during any early runaway greenhouse phase is short-lived, because the molten surface absorbs most oxygen liberated from H2O photolysis.

However, loss of a planet’s atmospheric cold trap remains a significant route to abiotic O2 after the host star arrives on the main sequence, highlighting the importance of obtaining observational constraints on this process. In all cases, exoplanets that receive lower stellar fluxes and/or have higher mass, such as LHS1140b and TRAPPIST-1g, have the lowest probability of abiotic O2 buildup. Key remaining uncertainties can be overcome in future by a combination of experiment, theory and (perhaps most critically) observational characterization of the atmospheres of hot, sterile exoplanets such as GJ1132b and TRAPPIST-1b and -c.

R. Wordsworth, L. Schaefer, R. Fischer
(Submitted on 1 Oct 2017)

Comments: 26 pages, 15 figures, submitted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:1710.00345 [astro-ph.EP] (or arXiv:1710.00345v1 [astro-ph.EP] for this version)
Submission history
From: Robin Wordsworth
[v1] Sun, 1 Oct 2017 13:05:58 GMT (877kb,D)
https://arxiv.org/abs/1710.00345
Astrobiology