Cassini At Dione

The Cassini spacecraft recently took close-up images of Saturn's small moon, Dione. Dione happens to be about the same distance from Saturn as Earth's Moon is from Earth.

The images reveal an ice ball of a world, but they also show relatively few craters, That suggests cryovolcanism is at work-- that is, eruptions resurface Dione, but instead of molten lava, ice and perhaps liquid water do the deed. That process, in turn, implies heat and energy at the moon's core. The driver of that energy is no doubt Saturn's powerful gravity, which constantly acts on Dione as the moon orbits the planet.