Mass-radius diagram for small transiting planets around M dwarfs, colour-coded according to equilibrium temperature T_eq. The TOI-406 planets are labelled, and highlighted with coloured diamonds. The sample was taken from the PlanetS catalogue (Parc et al. 2024) on July 30, 2024, reporting only planets with mass and radius determinations better than 25% and 8%, respectively. The solid green line indicates the theoretical composition models of Zeng et al. (2019) for an Earth-like composition (mass fractions of 32.5% iron and 67.5% silicates). The dotted dark blue lines correspond to Zeng et al. (2019) theoretical tracks of Earth-like rocky cores with H/He atmospheres by different percentages in mass at 300 K. The dotted orange line shows Rogers et al. (2023) mass-radius distribution derived from photoevaporation models. Dotted purple lines show Turbet et al. (2020) models for steam atmospheres, and the dash-dotted blue lines show Aguichine et al. (2021) compositional tracks at 400 K with a varying water mass fraction.