Whizzing around within the ring system, Dione orbits in 2.74 days. Its surface is marked by ice cliffs and impact craters. Saturn's fourth-largest moon, it shares its orbit with two small, irregularly shaped moons—Helene moving ahead of it, and Polydeuces behind.

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missions to saturn

Four craft have journeyed to Saturn. The first three, Pioneer 11, which arrived in 1979, and Voyagers 1 and 2 (1980 and 1981) were all flyby missions. The fourth, Cassini—Huygens, is a sophisticated orbiter designed to make a 4-year in-depth study of Saturn and its rings and moons. It is a joint American-European venture and consists of two probes, Cassini, the main probe, and the smaller Huygens, which was attached to Cassini for the journey to Saturn.

Cassini—Huygens arrived at Saturn in mid-2004, after a 7-year journey. As Cassini made its third orbit of Saturn, it released Huygens on its 21-day journey to Titan, where it descended to the moon's surface. In all, Cassini will make 74 orbits of Saturn, 44 close flybys of Titan, plus flybys of other moons before the mission's scheduled end in July 2008.

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