Shear heating on Enceladus

Plumes of water vapour and other gases escape at high velocities from the surface of Saturn's moon Enceladus, as is shown in this artist's concept.

The 'shear heating' mechanism suggests that tidal forces acting on fault lines in the moon's icy shell cause the sides of the faults to rub back and forth against each other, producing enough heat to transform some of the ice into plumes of water vapour and ice crystals. Cold sub-surface ice (depicted in blue) becomes much warmer near the active fractures from which the plumes emanate.