Mass–radius relationships (left axis) computed with the DROP code in the single layer case, for iron (purple), perovskite (green), and water (cyan), and for three flattening parameters, f ∈> {0,0.1,0.2}. Values of the input parameter A are indicated along the curves for f = 0, as described in Eq. (8). The domain where the fits are performed is indicated (grey-shaded zone) as well as the absolute error (right axis). The result obtained with ρ_s = 1 g/cm³, f = 0 and A = 0.6 for water in Eq. (4) is shown for comparison (cyan open circle). Also plotted are the empirical relationship valid in the range 1-8 M_⊕ and built from the Earth’s model by Zeng et al. (2016) (black crosses), the data from Table B.1 of Haldemann et al. (2020) obtained from the AQUA-EoS for water assuming a 300 K surface temperature (thin, dotted lines) and the results by Fortney et al. (2007) for pure-water and pure-silicate planets (open and filled squares), all obtained in the static case. See Sect. 6 for a discussion about LHS 1140 b (red dot).