A Validated Low-to-Intermediate Mass Planetary Interior Structure Model and New Mass-Radius Relations

TL;DR

This paper introduces a comprehensive planetary interior structure model incorporating advanced physics, validated against known planetary data, and provides extensive mass-radius relations for various planet types, aiding interpretation of observational data.

Contribution

The authors develop a new, physics-rich interior structure model that accurately replicates planetary properties and generates extensive mass-radius relations for diverse exoplanet compositions.

Findings

Model replicates Earth's radius and inertia within 0.2%

Mass-radius relations are provided for planets from 0.01 to 100 Earth masses

Radii predictions differ from literature, highlighting the need for advanced models

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 $0.2\%$, Mars and the Moon's to within $0.5\%$, and Mercury, Venus, and Europa's to within $1\%$ 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 $0.01-100\, M_\oplus$. We calculate mass-radius tables and fit piece-wise power-laws to them for ${<}8M_\oplus$ planets, finding that the exponent in $M=aR^b$ 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 32,971 model planets are publicly available.