Mass versus density diagram of confirmed exoplanets as a function of orbital period. Density is relative to an Earth-like interior ρ_Earth-scaled that corresponds to a planetary mass M_p. Molten mantles alone can lower the bulk density to ρ_p/ρ_Earth-scaled = 0.87. All planets are close-in such that irradiation and tidal heating may prohibit complete solidification. Planet sample is taken from the TEPCat catalogue (http://www.astro.keele.ac.uk/jkt/tepcat/) and shows planets with radii less than twice Earth (R_p < 2R_⊕), and mass and radius uncertainties below 35 and 15%, respectively.