Small-planet evolution mediated by atmospheric fractionation and magma ocean evolution

The Kepler and TESS exoplanet surveys have taught us that the most common planetary formation pathway leads to sub-Neptunes: planets larger than Earth and smaller than Neptune. Our Solar system contains no sub-Neptunes, and their compositions remain poorly understood. I developed an atmospheric escape model, IsoFATE, and coupled it to the magma ocean/equilibrium chemistry model, Atmodeller, to understand how sub-Neptunes evolve over time. I present recent results that show a gradient in planetary oxidation spanning the bimodal radius distribution separating rocky planets from those that retain atmospheres. I also present results from an observational survey that tests predictions of helium-enriched atmospheres, revealing the first atmosphere detection on a temperate, rocky exoplanet.