Enceladus. Computer artwork of a geyser erupting on the surface of Enceladus, the sixth-largest moon of Saturn. Enceladus is a frozen world with a surface consisting mostly of water ice. Tidal forces from Saturn's massive gravity alternately pull and push on Enceladus' interior, creating enough heat to melt the water ice immediately beneath the surface. This heated water is thought to periodically erupt like a volcano, a process known as cryovolcanism. Saturn itself appears low on the horizon due to the proximity to Enceladus' pole. The small object immediately to Saturn's left is another icy moon called Mimas.