December 5, 1999
The oldest light in the universe still hums faintly through space, a relic of the beginning itself.
Rhea: Saturn's Second Largest Moon
Birthday · December 5, 1999
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APOD published December 5, 1999. Credit: Calvin J. Hamilton. A publication-date match, not a photo taken on your date. Independent of NASA.
Rhea is the second largest moon of Saturn, behind Titan, and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. 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. The above photograph was taken with the Voyager 1 spacecraft in 1980.
Image credit: Calvin J. Hamilton