Scientists have suspected for a while that Saturn's moon Enceladus has a giant water ocean, and they now have some hard evidence to support their theories. Thanks to the Cassini spacecraft, NASA has discovered a "very slight wobble" in the moon that can only be explained by a global ocean that lets the icy crust move. Think of it like shaking an egg -- the changes in Enceladus' speed during orbit make its surface (the shell) shift around its rocky core (the yolk).
There are still some mysteries left, including why Enceladus' ocean is relatively warm. It's possible that Saturn's tidal forces are warming the moon more than possibly thought. No matter what, you're going to learn more about this celestial body in the near future. Cassini is conducting a very close (30 miles) flyby of Enceladus on October 28th, giving researchers the kind of data they've wanted for years.
[Image credit: NASA/JPL-Caltech]