Mass-radius diagram and TSM for TOI-2136b. Left panel: mass and radius values for known exoplanets (data taken from TEPcat database. Southworth 2011). The position of TOI-2136b is marked by the red star. In the figure we only show planets having mass measurements with a precision better than 30%. The lines represent theoretical mass-radius relationships for five different bulk compositions, including bare rocky planets with an Earth-like composition, pure water worlds, and Earth-like rocky cores with 0.1%, 1%, and 5% H + He envelopes with radiative equilibrium temperature of 400 K (see text). The orange points represent planets orbiting M-type stars, and the gray squares are planets around other types of stars. Right panel: apparent magnitude in J-band vs. the TSM by Kempton et al. (2018) for TOI-2136b and known transiting planets with radii smaller than 4R_⊕. The other labeled planets are the hycean candidates.