Active volcanism has been known to exist on just three solar system bodies — Earth, Jupiter’s moon Io, and possibly Neptune’s moon Triton. Now Cassini scientists have proposed another member of this exclusive club. The Cassini spacecraft may have found evidence of liquid water reservoirs that erupt in Yellowstone-like geyers on Saturn’s moon Enceladus. High-resolution images of the warm south polar region show icy jets and towering plumes ejecting large quantities of particles at high speed. Why is Enceladus so active? And why is the south pole so hot? The answer might be the effects of tidal forces that squeeze and stretch the moon as it orbits Saturn. Warm, low-density material rising to the surface could have literally caused Enceladus to roll over, putting the mass of warm material at the south pole.