Rhea: Saturn's Second Largest Moon . ... Credit Copyright: NASA , Voyager , Copyright Calvin J. Hamilton Explanation: Rhea is the second largest moon of Saturn , behind Titan , and the largest without an atmosphere. ... Rhea 's rotation and orbit are locked together (just like Earth's Moon) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea's leading surface is much more heavily cratered than its trailing surface. ...