Mass–radius diagram for the TRAPPIST-1 planets, Earth, and Venus. Curves trace idealised compositions of rocky and water-rich interiors (surface temperature fixed to 200 K). Median values are highlighted by a black dot. Coloured contours correspond to significance levels of 68% and 95% for each planet. The interiors are calculated with model II of Dorn et al. (2017). Rocky interiors are composed of Fe, Si, Mg, and O, assuming different bulk ratios of Fe/Mg and Mg/Si. U17 refers to Unterborn et al. (2018). Equilibrium temperatures for each planet are indicated by the coloured contours.