Enceladus, one of the moons of Saturn, photographed by Voyager 2, 1981

Enceladus, one of the moons of Saturn, photographed by Voyager 2, 1981. The surface of this, the 8th of Saturn's moons, is mostly water ice. The presence of grooves and smooth plains with a relatively small number of impact craters suggests that the surface of Enceladus is relatively young and indicates possible volcanic activity. The volcanic activity may be due to tidal effects caused by Dione, Saturn's 7th moon, heating the interior of Enceladus. A similar relationship between Europa and Io, two of Jupiter;s moons, is partly responsible for making Io the most volcanically active body in the Solar system. NASA's two Voyager spacecraft were launched in 1977 to explore the planets in the outer solar system. Voyager 2 passed Saturn in August 1981, before continuing on to Uranus and Neptune. ©SSPL/NASA