Atmospheres of Venus-like Planets: Stability Constraints on Mineral Reaction Buffers

The composition of a planet’s atmosphere can be buffered by chemical reactions with minerals at its surface [1-5]. The compositions of ‘hot’ thick exoplanet atmospheres can therefore act as probes of their planets’ surface mineralogies and compositions. In the context of a planetary atmosphere, however, many potential buffering reactions are not stable and would lead to catastrophic greenhouse runaway or atmospheric collapse. Introduction: In our solar system, mineralatmosphere buffering is most relevant for Venus [2-5]. The T and CO2 pressure at Venus’ surface match a point on the mineral decarbonation equilibrium, Calcite + Quartz = Wollastonite + CO2 CaCO3 + SiO2 = CaSiO3 + CO2 (Fig. 1), which has been suggested to buffer the CO2 content of Venus’ atmosphere [1-5]. The concept of atmospheric buffering by the surface has been applied to other gas species, such as sulfur gases, halogens, oxidation state (e.g., CO/CO2), etc. [2-6]. This particular reaction, calcite-quartz-wollastonite