The mass-radius relation of exoplanets, revisited

TL;DR

This paper re-analyzes the mass-radius relation of exoplanets using reliable data, identifying distinct regimes for small, intermediate, and massive planets, and pinpointing the transition radius between small and intermediate planets.

Contribution

It provides updated, precise mass-radius relations and transition points for different exoplanet categories based on a curated dataset.

Findings

Small planets have R ∝ M^{0.27} up to 4.4 M_⊕.

Intermediate planets follow R ∝ M^{0.67} between 4.4 and 127 M_⊕.

Gas giants exhibit R ∝ M^{-0.06} beyond 127 M_⊕.

Abstract

Determining the mass-radius ($M$-$R$) relation of exoplanets is important for exoplanet characterization. Here we present a re-analysis of the $M$-$R$ relations and their transitions using exoplanetary data from the PlanetS catalog which only includes planets with reliable mass and radius determinations. We find that "small planets" correspond to planets with masses of up to $\sim4.4 M_\oplus$ (within 17%) where $R \propto M^{0.27}$. Planets with masses between $\sim4.4$ and $127 M_\oplus$ (within 5%) can be viewed as "intermediate-mass" planets, where $R \propto M^{0.67}$. Massive planets, or gas giant planets, are found to have masses beyond $127 M_\oplus$ with an $M$-$R$ relation of $R \propto M^{-0.06}$. By analyzing the radius-density relation we also find that the transition between "small" to "intermediate-size" planets occurs at a planetary radius of $\sim1.6 R_\oplus$ (within 3%). Our results are consistent with previous studies and provide an ideal fit for the currently-measured planetary population.