Radius and mass distribution of ultra-short period planets

Ultra-short period (USP) planets are an enigmatic subset of exoplanets defined by having orbital periods < 1 day. In this study, we use updated stellar properties incorporating Gaia DR2 parallaxes to revise the radii of and compute occurrence rates for USP planets. We then derive a mass distribution for USP planets using planet interior structure models that take into account tidal distortion. The radius and mass distributions of USP planets provide insights into planet formation and the core mass distribution of longer period planets that retain hydrogen-dominated envelopes.