Iapetus: Saturn’s Stained Moon

Color image of Iapetus captured by Cassini on March 11, 2017 (NASA/JPL-Caltech/SSI/Jason Major)

Saturn’s “yin-yang” moon Iapetus (pronounced eye-AH-pe-tus) is seen in this image, a color composite made from raw images acquired by Cassini’s narrow-angle camera on March 11, 2017.

The color difference on Iapetus is due to a fine coating of dark material that falls onto its leading hemisphere, sent its way by the distant moon Phoebe traveling within the recently-discovered giant diffuse ring. This dark coating of dust causes that half of Iapetus’ surface to warm up ever-so-slightly-more than the other, making the underlying water ice evaporate and redeposit on the other side. This in turn reinforces the cycle…a positive feedback loop.

Stains of dark material on Iapetus’ icy surface, imaged by Cassini in 2007. (Color-composite by J. Major.) NASA/JPL/SSI

Iapetus is 914 miles (1,471 km) in diameter, or about as wide as Texas and Louisiana combined. It orbits Saturn at a considerable distance of 2,212,889 miles (3,561,300 km), which is nine times farther from Saturn than the Moon is from Earth.

Both halves of Iapetus feature single prominent impact craters and a miles-high mountainous ridge around its equator. See high-res color images of both sides of Iapetus here.

The 12-mile (20 km) high central ridge of Iapetus, a.k.a. the Voyager Mountains (NASA/JPL/SSI)

Learn more about Iapetus here.

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