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This almost surreal view of Iapetus was acquired by Cassini about 10 minutes after the spacecraft's closest approach to the icy moon during a close flyby on New Year's Eve 2004. The image shows Iapetus' surface illuminated by reflected light from Saturn (not by the Sun) and is the highest resolution view acquired to date of this part of Iapetus' surface. Compared to the approximately one second exposure times used for imaging Iapetus' sunlit side, this view required a very long exposure time of 82 seconds. Cassini was designed to pivot while moving in order to keep its cameras and other remote sensing instruments pointed 'on target' with great precision. Consequently, despite the large relative speed between Iapetus and the spacecraft during this long exposure -- about 2 kilometers per second or almost 4,500 miles per hour at closest approach -- the image of the moon?s surface is un-smeared (although the background stars are smeared). This image reveals a heavily cratered surface and shows the boundary between Iapetus' bright trailing hemisphere and Cassini Regio -- a large, dark region that covers the leading hemisphere of the moon?s surface. Some of the dark material appears to have collected inside the rim of a large impact structure about 250 kilometers across (155 miles) that lies just beyond the edge of the dark region (seen here near the right of the image). NASA's Voyager images (see
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