Growth And Evolution Of Secondary Volcanic Atmospheres: I. Identifying The Geological Character Of Warm Rocky Planets

(a) Model schematic and (b) flowchart. Arrows in (b) show direction of information flow

The geology of Earth and super-Earth sized planets will, in many cases, only be observable via their atmospheres. Here, we use the creation of volcanic atmospheres as a key window into planetary geochemistry.

We couple volcanic outgassing with atmospheric chemistry models to simulate the growth of C-O-H-S-N atmospheres in thermochemical equilibrium, aiming to establish what information about the planet's mantle fO2 and bulk silicate H/C ratio can be determined by atmospheric observation. Warm (800 K) volcanic atmospheres develop distinct compositional groups as the mantle fO2 is varied, which can be identified using sets of (often minor) indicator species: Class O, representing an oxidised mantle and containing SO2 and sulfur allotropes; Class I, formed by intermediate mantle fO2's and containing CO2, CH4, CO and COS; and Class R, produced by reduced mantles, containing H2, NH3 and CH4.

These atmospheric classes are largely independent of the bulk silicate H/C ratio. However, the H/C ratio does affect the dominant atmospheric constituent, which can vary between H2, H2O, CO2 and CH4 once the chemical composition has stabilised to a point where it no longer changes substantially with time. This final state is dependent on the mantle fO2, the H/C ratio, and time since the onset of volcanism. Superchondritic H/C enrichment to the level of Earth (H/C = 0.99 +/- 0.42) and higher can only be inferred for planets with reduced mantles producing Class R atmospheres. On warm, volcanically active planets, mantle fO2 could be identifiable from atmospheric observations using JWST.

Philippa Liggins, Sean Jordan, Paul B. Rimmer, Oliver Shorttle

Comments: Submitted to JGR:Planets
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)
Cite as: arXiv:2111.05161 [astro-ph.EP] (or arXiv:2111.05161v1 [astro-ph.EP] for this version)
Submission history
From: Philippa Liggins
[v1] Tue, 9 Nov 2021 14:18:40 UTC (3,534 KB)

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