The Super-Earth to Sub-Neptune Fraction as a Function of Stellar Age

By studying exoplanet demographics we can shed light on interesting patterns in planetary systems, such as the radius valley; a scarcity of planets between 1.5 and 2.0 Earth radii. The formation of this bimodal distribution of planetary radii has been heavily debated with X-ray + UV irradiation and core-powered mass loss being two leading explanations. In this work, we investigate the influence of age on the fraction of super-Earths to sub-Neptunes using the CKS (California Kepler Survey) sample. Our analysis accounts for stellar age and planet radius uncertainties, the orbital period dependence of the radius valley (and its uncertainty), and the effects of varying small planet sensitivity as a function of age. We also explore the sensitivity of our analysis to several data reliability cuts. We tentatively find that the fraction of super-Earths to sub-Neptunes increases on Gyr timescales which is consistent with atmospheric mass loss, but is in tension with the 100 Myr timescale often associated with X-ray + UV driven photoevaporation.