Buy this image Iapetus Two Dark Sides space photo.
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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 (1,468 kilometers, or 912 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.
Addition Date: December 26, 2005
Image Credit: NASA/JPL/Space Science Institute