Europa's Subsurface Ocean: Tidal Heating, Hydrothermal Energy, and the Search for Life
To the point
Europa probably has a salty ocean beneath its ice, heated mainly by tides, with possible hydrothermal activity that could support life from chemical energy, similar ideas apply to Enceladus and Mars, and the Europa Clipper mission is planned for 2030 to study the ice shell and ocean to assess habitability.