Atmospheric evolution of rocky planets around M dwarfs is shaped by interior redox processes

Rocky exoplanets around M dwarfs have been investigated by many theoretical and observational studies in the recent years. In contrast to close-in, hot rocky exoplanets often termed "exo-Venuses", recent observational campaigns suggest that many of these planets may either not posses an atmosphere, or only a very thin atmosphere either full of hazes or not made of CO2, therefore not resembling Venus.

 

In this study we aim at predicting possible atmospheric evolutionary pathways of such planetary atmospheres starting from compositional and evolutionary constraints of the star-planet system (including redox profiles in the interior set by core formation). We then model the evolution of the atmospheres depending on outgassing from the interior, atmospheric chemical equilibrium, greenhouse effects, water condensation incl. the atmospheric cold trap, solubility of volatiles in the melt, and atmospheric escape.

 

We show that depending on various key factors such as planetary mass, initial bulk redox state, magma ocean evolution and atmospheric escape efficiency, different types of atmospheres are predicted, with CO2-dominated, Venus-like atmospheres being restricted to specific scenarios, only, while in other scenarios for example bare-rock atmospheres or thin N2-O2-dominated, abiotically generated atmospheres will be more likely, suggesting a wide diversity of "exo-Venus" atmospheres.