The case for secondary atmospheres on temperate rocky planets around M-dwarfs

Early JWST observations of hot rocky exoplanets have revealed that many of these objects may be airless rocks. For example, JWST observations of TRAPPIST-1b [1] and c [2] disfavor substantial atmospheres containing CO2. Given the similar densities of all TRAPPIST-1 planets, and the theoretical potential for atmospheric erosion around late M-dwarfs, this observation might be assumed to imply atmospheres are also unlikely for the outer planets. Here, we present a new, self-consistent model of atmosphere-interior evolution during the transition from primary to secondary atmospheres to show that this may not be the case. The model incorporates all Fe-C-O-H-bearing species and simulates magma ocean solidification, radiative-convective climate, thermal escape, and mantle redox evolution. For our illustrative example TRAPPIST-1, our model strongly favors atmosphere retention for the habitable zone planet TRAPPIST-1e. In contrast, the same model predicts a comparatively thin atmosphere for the Venus-analog TRAPPIST-1b, which would be vulnerable to complete erosion…