Mass-radius diagram of small exoplanets (with radii ranging from 1–4 R_⊕) with precise densities from the PlanetS catalog. The red (gray) dots correspond to exoplanets orbiting M dwarfs (FGK dwarfs). The composition lines of pure silicates (yellow dashed), Earth-like planets (red dashed), and pure iron (solid black) from Zeng et al. (2016, 2019) are displayed. The red hexagon represent TOI-756 b. Two compositions line that incorporate both water and terrestrial elements from Aguichine et al. (2021) models, matching the equilibrium temperature of the planet, are plotted as light and dark blue dotted lines. Two compositions of Earth with an hydrogen-rich atmospheres from Zeng et al. (2019) are represented in pink and purple dotted lines. This plot has been generated with mr-plotter (https://github.com/castro-gzlz/mr-plotter/).