tidal heating

Tidal heating is the frictional heating of a moon's interior due to flexure caused by the gravitational pull of its parent planet and possibly neighboring satellites. The most dramatic example in the solar system is the tidal heating induced in each of the four Galilean satellites by their mutual pull and, more significantly, by the powerful attraction of Jupiter. In the case of Io, the result is global volcanism. In the case of Europa, and perhaps also of Ganymede and Callisto, the effects of tidal heating are less dramatic but possibly much more profound in that they give rise to a suspected under-ice ocean which might conceivably support life.