Volume: 03, Issue: 01 01/12/2005 
This stereo view of Iapetus was created by combining two Cassini images, which were taken one day apart. Image courtesy NASA/JPL/Space Science Institute.
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On New Year's Eve 2004, Cassini flew past Saturn's intriguing moon Iapetus, capturing the four visible light images that were put together to form this global view. Image courtesy NASA/JPL/Space Science Institute.
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This near-true color view from Cassini reveals the colorful and intriguing surface of Saturn's moon Iapetus in unrivaled clarity. Image courtesy NASA/JPL/Space Science Institute.
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Tsunami-Causing Earthquake Changed Rotation of Earth
Deep Impact Heads for Comet Collision
Hubble Providing Evidence of Possible New Planet
Participate in Professional Development Offerings

Cassini Reveals Bulging Waistline of Iapetus

NASAís Cassini spacecraft flew by Saturnís moon Iapetus (eye-APP-eh-tuss) on New Yearís Eve, returning images that exhibit startling features on the moon. These unique features are fueling heated scientific discussions about their origin.

One of these features is a long narrow ridge that lies almost exactly on the equator of Iapetus, bisecting its entire dark hemisphere and reaching 20 kilometers (12 miles) above the surface. It extends more than 1,300 kilometers (808 miles) wide. No other moon in the solar system has such a striking geological feature.

In certain areas, this mysterious ridge is comprised of mountains. They rival the height of Olympus Mons on Mars, approximately three times the height of Mt. Everestósurprising for such a small body. Mars is nearly five times the size of Iapetus, Saturnís third largest moon, which measures roughly 1,400 kilometers (890 miles) in diameter.

Jean-Dominique Cassini discovered Iapetus in 1672, noting that the moon is two-toned. Cassini, for whom the Cassini-Huygens mission is named, correctly deduced that the leading hemisphere of Iapetus is dark, while the trailing side is white.

The flyby images reveal a region of Iapetus never before seen. They show feathery-looking black streaks at the boundary between dark and bright hemispheres, indicating that dark material has fallen onto Iapetus. Opinions differ as to whether this dark material originated from within or outside Iapetus. The images also show craters near this boundary with bright walls facing toward the pole and dark walls facing towards the equator.

Cassini's next close encounter with Iapetus will occur in September 2007. The resolution of images from that flyby should be 100 times better than the ones currently being analyzed. The hope is that the increased detail may shed light on Iapetus' amazing features and the question of whether it has been volcanically active in the past.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C.

Images from Cassiniís flyby of Iapetus are available at the following websites:

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