From Earth-sized to Super-sized, the importance of planetary mass for atmospheric retention

To this day, there has not yet been any definitive detection of an atmosphere around an Earth-sized planet. Most of these observations are of planets orbiting M-dwarfs very close-in, where conditions are much harsher than at an Earth-like distance from a Sun-like star. Both thermal and non-thermal loss processes are likely much more effective in removing the atmospheres of these M-dwarf Earth-sized planets. However, the existence of Hot-Jupiters demonstrates that large atmospheres can be retained around massive enough close-in planets. Even in our own Solar System we can see the importance of planetary mass to atmospheric retention when we look at Earth and its two neighbours.

In this work we explore how the mass of close-in exoplanets affects the loss of secondary atmospheres. We achieve this by using the Kompot code, a 1D self-consistent thermo-chemical code, to model various CO2/N2 upper atmospheres from first principles. These models allow us to calculate the Jeans escape, a type of thermal escape. We then combine these loss calculations with models of various stellar types to determine which planet-star combination is most likely to retain an atmosphere. These results are particularly useful to select targets for observations with large instruments such as JWST.