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Color image of Iapetus cratered light and dark surface
Voyager 2 photographed Iapetus in 1981.
Saturn: Moons: Iapetus

Two-faced Iapetus (eye-AP-eh-tuss) is one of Saturn's strangest moons. Half of it is as dark as asphalt, while the other half is as bright as snow. The dark half faces forward as Iapetus moves in its nearly circular, inclined orbit around Saturn. Scientists generally believe that it has swept up the orbiting dark material (perhaps originally from Phoebe) that covers its forward-facing surface. The light side is four to five times brighter than the dark side.

When Giovanni Cassini first discovered Iapetus using a telescope in 1671, he could only see the bright side of the moon. NASA's Voyager 2 flew past Iapetus on Aug. 22, 1981. Passing at a relatively distant 966,000 km (600,000 miles), the spacecraft's cameras could make out few details in the area of dark material. The images revealed the bright side to be icy and heavily cratered.

Scientists hope the advanced instruments and cameras on board the Cassini spacecraft will shed more light on this mysterious moon.

Iapetus in Mythology
Saturn was named for the Roman god of agriculture, but many of the planet's moons are named for the Titans and Titanesses of Greek mythology. They are the brothers and sisters of Kronos, Saturn's Greek counterpart.

A Titan and the father of Atlas, Iapetus was also the father of three Titans who judged the souls of the dead in Hades: Menoetius, Prometheus, and Epimetheus. Iapetus fought Zeus in the war between the Titans and the Olympian gods. He was vanquished and imprisoned with the other Titans after they lost that war.
Just the Facts
Distance from Saturn: 
3,561,300 km
Equatorial Radius: 
718 km
1,600,000,000,000,000,000,000 kg
Saturn's Moons
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Last Updated: 05.26.04