Mystery of Saturn's Two-Faced Moon Solved

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Mystery of Saturn's Two-Faced Moon Solved
This false-color mosaic shows the entire hemisphere of Iapetus acquired by Cassini. The transition region between the dark leading and bright trailing hemispheres is visible along the right side of the image. (Image credit: NASA/JPL/Space Science Institute)

Saturn'smoon Iapetus has virtually no gray. Rather, its features are all stark blackand white. The appearance has long puzzled astronomers.

Newdetailed images suggest sunlight is melting ice on one side of Iapetus, leavingthe moon's dark surface exposed, while the opposite half retains its reflectiveice-mixed shell.

Since themoon's discovery by Giovanni Domenico Cassini in 1671, Iapetus' appearance hasbaffled astronomers. The leading edge of Iapetus, which faces the direction ofits orbit, is black as asphalt, while its trailingside appears bright as snow. Iapetus is 907 miles (1,460 kilometers) wideand circles Saturn at a distance of about 2.2 million miles (3.6 millionkilometers).

The newobservations add support to a two-part explanation for Iapetus' appearance. First,as Iapetus treks around Saturn, itsleading edge scoops up a thin coating of dark material, which amplifiessunlight absorption.

Jeanna Bryner
Jeanna Bryner
Jeanna is the managing editor for LiveScience, a sister site to SPACE.com. Before becoming managing editor, Jeanna served as a reporter for LiveScience and SPACE.com for about three years. Previously she was an assistant editor at Science World magazine. Jeanna has an English degree from Salisbury University, a Master's degree in biogeochemistry and environmental sciences from the University of Maryland, and a science journalism degree from New York University. To find out what her latest project is, you can follow Jeanna on Google+.