Sample on the mass–density diagram. The black spheres represent the sample’s planets and the red spheres are the Solar System planets, plotted for comparison. Dashed black lines connect a pair of adjacent planets in the “high correlated in radius” subsample. The coloured interior curves (from red to light blue) are taken from Zeng et al. (2016) and correspond to different calculated MRR for several potential 2-layer structures of exoplanets, representing different combinations of constituents of the interior: Fe, MgSiO₃, and H₂O. The error bars are plotted for planets comprising the “high correlated in radius” subsample and omitted for others for the sake of clarity.