is an icy body similar in nature to Dione and Rhea. The density of Tethys is 1.21 gm/cm3, indicating that it is composed almost entirely of water-ice. Tethys's icy surface is heavily cratered and contains cracks caused by faults in the ice. The terrain is composed of densely cratered regions with a lightly cratered, dark belt that extends across the satellite. Light cratering indicates that Tethys was once internally active, causing parts of the older terrain to be resurfaced. The exact cause for the dark belt is unknown, but a possible interpretation comes from recent Galileo images of Jupiter's moons Ganymede and Callisto. Both satellites exhibit light polar caps that are made from bright ice deposits on pole-facing slopes of craters. From a distance the caps appear brighter due to a haze caused by thousands of unresolved ice patches in small craters. Tethys' surface may have been formed in a similar manner, consisting of hazy polar caps of unresolved bright ice patches with a darker zone in-between. 


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