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Rhea
The icy, cratered surface of Saturn's moon Rhea is seen in this high-resolution image from the Cassini probe. The heavily cratered surface attests to the satellite's ancient age. The largest craters, 50 to l00 kilometers (30 to 60 miles) across and several kilometers deep, are freshly preserved in Rhea's icy crust. The craters and landscape resemble those on the Moon and Mercury, and are unlike the flattened crater forms that have collapsed in the soft icy crusts of the Jovian moons Callisto, Ganymede and Europa. Scientists believe that Rhea froze and became rigid, behaving like a rocky surface, very early in its history. Rhea is just l,600 kilometers (995 miles) in diameter, compared to the 5,500-kilometer (3,400-mile) diameter of Ganymede,
