  In this study we investigated the interiors of rocky exoplanets in order to
identify those that may have large quantities of water. We modelled the
interiors of 28 rocky exoplanets, assuming four different layers - an iron
core, a rock mantle, a high-pressure ice layer, and a surface ice/water layer.
Due to observational bias, our study is limited to habitable zone exoplanets.
We determined a range of possible water mass fractions for each planet
consistent with the modelled planetary structures. We calculated the tidal
heating experienced by these exoplanets through gravitational interactions with
their host stars, assuming a temperature- and composition dependent Maxwell
viscoelastic rheology. Assuming radioactive elemental abundances observed in
Solar System meteorites, we also calculated the radiogenic heat flux inside the
planets. We estimated the probability of the presence of a thick ocean layer in
these planets, taking into account the effect of both tidal and radiogenic
heating. Our results showed that Proxima Centauri b, Ross 128 b, Teegarden's b
and c, GJ 1061 c and d, and TRAPPIST-1 e may have an extended liquid water
reservoir. Furthermore, extremely high H2O-content of the exoplanets Kepler-62
f, Kepler-1652 b, Kepler-452 b, and Kepler-442 b suggests that these planets
may maintain a water vapour atmosphere and may in fact be examples of larger
ocean worlds. Upon the discovery of new rocky exoplanets beyond the habitable
zone, our study can be extended to icy worlds.
