What links the presence of subsurface liquid water oceans on both Europa and Enceladus?

Answer

They require sustained internal energy to prevent freezing solid.

Both Europa and Enceladus possess vast subsurface liquid water oceans that require a constant input of internal energy, primarily generated by tidal flexing, to keep the water from freezing solid.

What links the presence of subsurface liquid water oceans on both Europa and Enceladus?
GeologyastronomyPlanetary SciencemoonsTidal heating