Enceladus: Saturn's Soda Fountain

Enceladus is a small, icy moon of Saturn that is something of an overachiever. It shoots geysers of water vapor, nitrogen, CO2, and methane from vents that pop open around its south pole. Obviously there has to be some liquid water under the surface for this to happen, and since Saturn is rather far from the sun, the energy needed to keep some of the water liquid (and eject geysers into space) has to come from something else. Enceladus seems to have a rocky core (judging from its density), so some heat could come from radioactive decay of minerals in the core - but this isn't enough to account for the geysers and the temperatures measured around the south pole vents. Tidal forces from Saturn and Dione don't provide enough energy with its current orbit either. But somehow plucky little Enceladus is still firing away with those geysers...

I know what you're thinking: a giant alien nuclear reactor! Well sure, that could be it, but the Cassini scientists are still looking at natural solutions, like accumulated heat from earlier periods when its orbit could have been more more eccentric and tidal forces larger. In any case it's a pretty wild little ice moon.

These highlights are from an article by Carolyn Porco (Cassini imaging team leader) in the December Scientific American. The video is also from SciAm - it gives some background and provides some great animated visuals of Saturn's soda fountain.