A Joint Mass-Radius-Period Distribution of Exoplanets

The radius-period distribution of exoplanets has been characterized by the Kepler survey, and the empirical mass-radius relation by the subset of Kepler planets with mass measurements. We combine the two in order to constrain the joint mass-radius-period distribution of Kepler transiting planets. We employ hierarchical Bayesian modeling and mixture models to formulate four models with varying complexity and fit these models to the data. We find that the most complex models that treat planets with significant gaseous envelopes, evaporated core planets, and intrinsically rocky planets as three separate populations are preferred by the data and provide the best fit to the observed distribution of Kepler planets. We use these models to calculate occurrence rates of planets in different regimes and to predict masses of Kepler planets, revealing the model-dependent nature of both. When using models with envelope mass loss to calculate η_⊕, we find nearly an order of magnitude drop, indicating that many Earth-like planets discovered with Kepler may be evaporated cores which do not extrapolate out to higher orbital periods. This work provides a framework for higher-dimensional studies of planet occurrence and for using mixture models to incorporate different theoretical populations of planets.