Mass-radius diagram. Left panel: planetary masses and radii of the known transiting exoplanets. The colors of the planets correspond to their equilibrium temperatures. The iso-composition curves for differentiated planets (Zeng & Sasselov 2013) are described in the legend. Right panel: zoom-in of the same diagram in mass linear scale, displaying the different compositions that best match the mass and radius of BD+00 444 b with both differentiated and miscible interiors (Sect. 5.2).