Abstract

The James Webb Space Telescope will enrich our understanding of the atmospheres of sub-Neptunes and super-Earths, including potentially habitable worlds. I will discuss what determines which exoplanets retain atmospheres and oceans, and how exoplanet atmosphere compositions are shaped by elemental fractionation. Key processes that can shape habitable-exoplanet atmospheres include impact erosion, XUV-driven atmosphere loss, planetesimal contamination, and atmosphere-magma exchange. I will discuss sub-Neptunes, terrestrial exoplanets, and the worlds in between.