An artist's impression of plumes of water vapor and other gases escaping at high velocity from the surface of Saturn's moon Enceladus.

Tidal forces acting on fault lines in the moon's icy shell cause the sides of the faults to grind against each other and produce heat, producing plumes of water vapor and ice crystals which spew into surrounding space.

Enceladus is 505 km in diameter. It completes an orbit of Saturn in just under 33 hours. Movement along the fault lines may be about half a meter over the course of an orbit.