Density-mass diagram (density normalised by an Earth-like composition) as a function of equilibrium temperature (colour bar). Left panel: Planets orbiting stars of 0.1 M_⊙ (circles), 0.4 M_⊙ (squares), and 0.7 M_⊙ (diamonds). Right panel: Planets orbiting stars of 1.0 M_⊙ (circles), 1.3 M_⊙ (squares), and 1.5 M_⊙ (diamonds). Note: the colour bars span different ranges in the two panels. For both panels, black-bordered symbols indicate f_HHe < 1%, dark-grey 1 ≤ f_HHe ≤ 10%, and light-grey f_HHe > 10%. The dashed-lines show the compositional curves of Earth-like (brown), pure-silicate (orange), condensed water (blue), and steam worlds (light-blue). The grey-dotted lines correspond to radii of 1 and 4 R_⊕.