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- Title
Growth and Evolution of Secondary Volcanic Atmospheres: I. Identifying the Geological Character of Hot Rocky Planets.
- Authors
Liggins, Philippa; Jordan, Sean; Rimmer, Paul B.; Shorttle, Oliver
- Abstract
The geology of Earth and super‐Earth sized planets will, in many cases, only be observable via their atmospheres. Here, we investigate secondary volcanic atmospheres as a key base case of how atmospheres may reflect planetary geochemistry. We couple volcanic outgassing with atmospheric chemistry models to simulate the growth of C‐O‐H‐S‐N atmospheres in thermochemical equilibrium, focusing on what information about the planet's mantle fO2 and bulk silicate H/C ratio could be determined by atmospheric observation. 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 oxidized 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 robust to a wide range of bulk silicate H/C ratios. However, the H/C ratio does affect the dominant atmospheric constituent, which can vary between H2, H2O and CO2 once the chemical composition has stabilized to a point where it no longer changes substantially with time. This final atmospheric state is dependent on the mantle fO2, the H/C ratio, and time since the onset of volcanism. The atmospheric classes we present are appropriate for the closed‐system growth of hot exoplanets, and may be used as a simple base for future research exploring the effects of other open‐system processes on secondary volcanic atmospheres. Plain Language Summary: To understand the geology of rocky planets, we must learn to use observations of their atmospheres to infer the properties of their interiors. When rocky planets have atmospheres made up of gases released by volcanoes, the chemistry of the atmosphere can be linked back to the volatile content and availability of oxygen in the planet's interior. In order to understand what the atmospheres of these rocky planets might look like, we use computer simulations to analyze their evolution and chemical signatures. We find that planets with Venus‐like surface temperatures will produce atmospheres whose chemical compositions enable them to be split into three distinct categories. These three classes are identified using diagnostic combinations of species. Key Points: Varying the mantle fO2 of hot rocky planets can produce three distinct atmospheric classesThe planet's mantle fO2, H/C ratio and age control whether the main atmospheric species is H2O, H2 or CO2The chemical speciation of volcanic atmospheres is robust to a wide range of bulk silicate planet H/C mass ratios
- Subjects
VENUS (Planet); PLANETS; ATMOSPHERIC models; ATMOSPHERE; PLANETARY atmospheres; PLANETARY surfaces; ATMOSPHERIC chemistry
- Publication
Journal of Geophysical Research. Planets, 2022, Vol 127, Issue 7, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2021JE007123