2023ApJ...956...29Q

We have estimated total internal heating rates and depths to possible subsurface oceans for 17 planets that may be cold ocean planets, low-mass exoplanets with equilibrium surface temperatures and/or densities that are consistent with icy surfaces and a substantial H₂O content. We have also investigated the potential for tidally driven cryovolcanism and exosphere formation on these worlds. Estimated internal heating rates from tidal and radiogenic sources are large enough that all planets in our study may harbor subsurface oceans, and their geological activity rates are likely to exceed the geological activity rates on Jupiter's moon Europa. Several planets are likely to experience enhanced volcanic activity rates that exceed that of Io. Owing to their relatively thin ice shells and high rates of internal heating, Proxima Cen b and LHS 1140 b are the most favorable candidates for telescopic detection of explosive, tidally driven cryovolcanism. Estimates for thin ice shells on Proxima Cen b, LHS 1140 b, Trappist-1f, and several Kepler planets suggest that any H₂O vented into space during explosive cryovolcanic eruptions on these worlds could be sourced directly from their subsurface oceans. Like the icy moons in our outer solar system, cold ocean planets may be astrobiologically significant worlds that harbor habitable environments beneath their icy surfaces. These possibilities should be considered during analyses of observational data for small exoplanets from current and upcoming telescopes and during planning for a future space telescope mission aimed at characterization of potentially habitable exoplanets (e.g., Habitable Worlds Observatory).