{ Moons of Saturn }
Discovered by            Giovanni Domenico Cassini
Date of Discovery        1684
Distance from Saturn     377,400 km
Radius                   560 km
Mass                     1.10 × 10^24 g
Orbital Eccentricity     0.002230
Orbital Inclination      0.02°
Orbital Period           2.736914742 days
Rotational Period        Synchronous
Density (gm/cm3)         1.43 

This icy moon is in most respects a twin of Rhea. It differs in that it is denser. In fact it is the densest of Saturn's moons besides Titan. Like Rhea, it has a hemisphere that is densely cratered, and one that isn't. It always has the same hemisphere facing Saturn.

One of the interesting features of this moon is that the heaviest cratering occurs on the leading hemisphere (in terms of its orbit) which is the opposite of what is expected from a satellite like Dione. Some scientists believe this is due to the satellite being spun, perhaps several times, by large meteor impacts. The presence of sufficiently large craters supports this theory.

Another interesting feature is that, like Tethys, Dione has a companion moon sharing its orbit. Helene, precedes Dione by about 60° as they orbit Saturn.


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