Atlas as viewed by the Cassini spacecraft in 2005-07. On the left, as seen from behind, with North on top; on the right, as seen from below its Equator, with the leading edge on the left, from a viewpoint four times closer to the moon. The left image shows a 2 to 3 mile high ridge circling the moon's Equator, while the right image shows that the ridge is much smoother than the regions to the South of it. The Cassini spacecraft imaged similar ridges on Iapetus and Pan, but the cause of the ridges, never before seen on any Solar System object, is currently a mystery. (Planetary Photojournal) |