Scaled densities and masses of observed exoplanets in comparison to curves of constant core radius fractions. Planet densities are scaled relative to an Earth-analogue of fixed core radius fraction (0.547) and for a given mass. The selected exoplanets are from the PlanetS database (Otegi et al. 2020) plus K2-38 b and Kepler-406 b (see main text). Earth (E), Venus (V), Mars (Ma), and Mercury (Me) are also shown. The emerging population of super-Mercuries with densities indicative of iron enrichment covers a range of masses up to 5-10 M_E.