A validated low-to-intermediate mass planetary interior structure model and new mass–radius relations

ABSTRACT The increasing precision of planetary mass and radius observations is bringing major questions about the structure and formation of planets – such as the nature of the radius valley and origin of super-Mercuries – within reach, demanding the development of interior structure models with more physics to more accurately determine planetary radii for a given composition. Here, we present a new model that includes state-of-the-art equations of state following the latest experimental and computational results, a physically motivated mineralogy allowing multiple species to coexist within planetary layers, a non-adiabatic temperature profile, melting, and other features. This model replicates Earth’s radius and moment of inertia coefficient to within $0.2{{\ \rm per\ cent}}$, Mars and the Moon’s to within $0.5{{\ \rm per\ cent}}$, and Mercury, Venus, and Europa’s to within $1{{\ \rm per\ cent}}$ or 3$\sigma$. We use this model to calculate mass–radius relationships for H/He-enveloped, water-rich, Earth-like, and iron-rich bodies with masses between 0.01 and $100\, \mathrm{ M}_\oplus$. We calculate mass–radius tables and fit piece-wise power laws to them for ${\lt }8\,\mathrm{ M}_\oplus$ planets, finding that the exponent in $M=bR^a$ increases with mass and core mass fraction. We find radii generally smaller than in literature mass–radius relations at low instellations and larger at high instellations, with our improvement on the literature comparable to observational uncertainties. State-of-the-art interior structure models are thus required to interpret observational data. Our mass–radius curves comprising 32 975 model planets are publicly available.