[link|http://www.spaceflightnow.com/cassini/060306iapetus.html|http://www.spaceflig...60306iapetus.html]

This image of the moon Iapetus shows two large craters, one that looks like it is illuminated from the left, and the other illuminated from the right. Actually, the lower large crater has whitish frosty stuff that landed on the right-facing slopes that only looks like light.

The source of the frosty stuff is unknown, but could be from water or ice gueysers caused by tidal heating or from a collision with a small icey moon.