CICLOPS: Cassini Imaging Central Laboratory for OPerationS

A Moon with Two Dark Sides
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Although it is no longer uncharted land, the origin of the dark territory of Cassini Regio on Iapetus remains a mystery. Also puzzling is the equatorial ridge that bisects this terrain, and how it fits into the story of the moon's strange brightness dichotomy. The ridge is seen here, curving along the lower left edge of Iapetus.

The view looks down onto the northern hemisphere of Iapetus (1,471 kilometers, 914 miles across), and shows terrain on the moon's leading hemisphere.

The image was taken in polarized green light with the Cassini spacecraft narrow-angle camera on Nov. 12, 2005 at a distance of approximately 417,000 kilometers (259,000 miles) from Iapetus and at a Sun-Iapetus-spacecraft, or phase, angle of 95 degrees. Image scale is about 2 kilometers (1 mile) per pixel.

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. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit and the Cassini imaging team home page,

Credit: NASA/JPL/Space Science Institute
Released: December 26, 2005 (PIA 07660)
Image/Caption Information
  A Moon with Two Dark Sides
PIA 07660

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