Dione is Saturn’s fourth largest moon with a diameter of 1,123 km and orbits Saturn every 2.7 days at a distance of 377,400 km, a similar distance to that of which the moon orbits the Earth. Unlike many of the other moons of Saturn, Dione is rather dense which suggests that around a third of the moon is made up of a rocky core (probably silicate rock) with the remainder being water ice. Data from Cassini suggests that Dione also has an internal liquid salt water ocean with an ice crust.
Very fine powdery ice from one of Saturn’s rings (which originally came from Enceladus) constantly bombards Dione. Dione’s surface features areas that are heavily cratered, moderately cratered, lightly cratered and fractured. Strangely the more heavily cratered areas are in the trailing hemisphere which suggests that one of the larger impacts may have spun the moon around. The fractured areas are ice cliffs that are hundreds of metres high.
