The moon is generally thought to be a dry place, and the discovery of water on its surface comes as an unexpected — and exciting — surprise for researchers. Carolina K. Smith/iStockphoto.com hide caption

itoggle caption Carolina K. Smith/iStockphoto.com

This radar image taken by Cassini in July 2006 of Titan, one of Saturn's moons, provides convincing evidence that it is covered by large bodies of liquid. NASA/JPL/Space Science Institute hide caption

itoggle caption NASA/JPL/Space Science Institute