NASA Astronomy Picture of the Day Collection

Ancient Craters on Saturn's Rhea

Saturn's ragged moon Rhea has one of the oldest surfaces known. Estimated as changing little in the past billion years, Rhea [ http://en.wikipedia. org/wiki/Rhea_(moon) ] shows craters [ http://en.wikipedia…] so old they no longer appear round ? their edges have become compromised by more recent cratering. Like Earth's Moon [ http://antwrp.gsfc.…], Rhea's rotation is locked on Saturn, and the above image [ http://photojournal…] shows part of Rhea's surface [ http://antwrp.gsfc.…] that always faces Saturn. Rhea's leading surface is more highly cratered than its trailing surface. Rhea [ http://antwrp.gsfc.…] is composed mostly of water-ice but is thought to have a small rocky core. The above image [ http://photojournal…] was taken by the robot Cassini spacecraft [ http://www.esa.int/…] now orbiting Saturn. Cassini swooped past Rhea two months ago and captured the above image from about 100,000 kilometers away. Rhea [ http://www.nineplan…] spans 1,500 kilometers making it Saturn's second largest moon after Titan [ http://antwrp.gsfc.…]. Several surface features on Rhea [ http://antwrp.gsfc.…] remain unexplained including large light patch [ http://antwrp.gsfc.…]es.

Cassini Imaging Team [ http://ciclops.org/], SSI [ http://www.spacesci…], JPL [ http://www.jpl.nasa…], ESA [ http://www.esa.int/], NASA [ http://www.nasa.gov/]

Saturn

Rhea

Goddard Space Flight Center (GSFC)

Jet Propulsion Laboratory (JPL)

Earth

Moon

Saturn

Cassini

Crater

Titan

Huygens Probe

Rhea

Cassini-Huygens

http://antwrp.gsfc.…

SPD-APOD-ap060530