Radius-density plot of planets with radii < 5 R_⊕ orbiting M dwarfs (here defined as having T_eff = 2380–3850 K) with 45% and 15% uncertainties or lower in mass and radius, respectively (57 planets in 38 systems). All planets except nine (the Trappist-1 and K2-146 systems) have masses from RV measurements. The density gap referred to in the text is clearly seen between 1.3 R_⊕ and 1.5 R_⊕ in radius and between 3.5 g cm⁻³and 8 g cm⁻³in density. The planets are colour-coded with instellation. The TOI-776 planets are marked with star symbols (planet b to the left and planet c to the right). The squares are (from left to right) the Solar System planets Mars, Venus, Earth, Neptune, and Uranus. Interior models from Zeng et al. (2019) are plotted as listed in the legend.