Mass-radius diagram of all currently known transiting exoplanets with mass determination (from RV or transit time variations), in comparison with the Solar System planets. Filled circles with error bars colour-coded by their host’s T_eff are planets with mass and radius uncertainties of less than 30%, and open grey circles are the others. The filled black star is Gl 486 b. Dashed coloured curves are theoretical models of Zeng et al. (2019), as specified in the legend. The Earth-like model is orange. The grey vertical dashed line is the deuterium burning mass limit at 13 M_Jup (‘planet’-brown-dwarf boundary; see Caballero 2018 and references therein). In the inset, we zoom in around the smallest planets and add mass-radius relationships informed by stellar abundances (Sect. 5.2). We plot median and 1σ error regions following nominal relative abundances of Fe, Mg, and Si of the host star without (pink) and with (cyan) the empirical correction of Adibekyan et al. (2021) based on well-characterised super-Earths. The two outliers with very high densities and M ~ 2.0 M_⊕ are Kepler-1972b and c, which are two transiting planets with masses determined from transit time variations (Leleu et al. 2022).