The mass-radius relation of exoplanets, revisited

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 $\sim 4.4M_{\oplus }$ (within 17%) where $R\propto M^{0.27}$. Planets with masses between $\sim 4.4$ and $127M_{\oplus }$ (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 $127M_{\oplus }$ 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 $\sim 1.6R_{\oplus }$ (within 3%). Our results are consistent with previous studies and provide an ideal fit for the currently-measured planetary population.