Atmospheric lifetime from a hypothetical Mars-sized planet orbiting Barnard’s Star

Atmospheric escape from exoplanets is a topic of great interest for the exoplanet community since atmospheric retention is an important component of surface habitability. While atmospheric escape has been detected from large exoplanets, it remains difficult to measure for smaller (rocky) planets. Indeed, for rocky planets orbiting active stars it is thought that it may be difficult for atmospheres to be retained at all. In the absence of detailed observations, one option is to leverage observations and models for planets in our own solar system.

Here we consider atmospheric escape from Mars – if it orbited an M Dwarf star similar to Barnard’s star. Our analysis considers five escape processes: hydrodynamic escape, thermal escape, photochemical escape, ion escape, and sputtering. To estimate the escape rate via each process from our hypothetical “ExoMars”, we employ models for escape that have either been validated using observations or verified against other models. We provide escape rate estimates for important species in the Martian upper atmosphere: O, O₂, H, and CO₂, and use them to estimate the lifetime of the Martian atmosphere.