Coupled atmospheric-ice sheet model for tidally locked exoplanets

Due to their cosmic abundance and long lifetimes, M-dwarfs are by far the most abundant stars in the Universe. Planets orbiting in the habitable zone of these stars are tidally locked, most likely in synchronous rotation, with crucial consequences for their climate and habitability. However, there is no analogue in the Solar System of such configurations and observations of terrestrial exoplanets remain challenging, leaving their climate and habitability to speculation.

We coupled a GCM of an Earth-like planet to a simple ice sheet elevation and bedrock deformation model, and assessed how much, and where, water ice is trapped on the permanent nightside; such ice trapping has previously been identified as a threat to the habitability of synchronously-rotating temperate terrestrial planets. We identified a strong feedback between snowfall rates and global ice elevation, and found that ice sheet elevation depends on the whole tropospheric temperature structure. We also revisited previous results of water trapping by estimating where ice sheets are limited by the amount of water available in the atmosphere rather than by basal melting. These results show that assessing the habitability of synchronously-rotating terrestrial planets requires sophisticated geophysical modeling, an endeavor still in its early days.