SCoRE: the Surface Composition of Rocky Exoplanets

Abstract

Context. The crust composition of rocky exoplanets with a substantial atmosphere can not be observed directly. However, recent developments are starting to allow for the observation and characterisation of their atmospheres. Understanding the link between atmospheres and crusts could allow for constraints on the crusts' composition based on atmospheric observations. Aims. We aim to understand the link between the thermal stability of specific condensates and atmospheric compositions. This allows constraints on the mineralogical composition of the surface by potentially observable atmospheric features. In order to achieve this, a grid study of atmospheric and crustal compositions is conducted. Methods. We use a diverse range of total element abundances inspired by various rock compositions as the compositional base for our crust-atmosphere models, for which thermo-chemical and phase equilibrium is assumed. In this work, we investigate a temperature range of 500 K to 1000 K and a surface pressure of 1 bar. The resulting atmospheric compositions are classified using atmospheric types based on the most abundant gas-phase elements C, H, N, O, and S. Results. Some of the changes in surface mineralogy coincide with changes in atmospheric type, independent of the given total elemental abundances. In total, a link has been revealed between 23 thermally stable minerals and their corresponding atmospheric types, which is independent of the ratio of the refractory elements present. Especially, the sulphur chemistry of the minerals and the average iron oxidation state can be constrained by the corresponding atmospheric type.