Enceladus orbits Saturn between the smaller Mimas and the larger Tethys . Enceladus is composed mostly of water ice and has the cleanest and purest ice surface in the Solar System . The surface also has many unusual groves and relatively few craters, like Jupiter 's moon Ganymede . To explain this, some astronomers speculate that Enceladus is susceptible to some sort of volcanic activity. Enceladus was originally discovered in 1789 by William Herschel .
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