Hyperion - Cosmic Blasting Zone
Flight to Hyperion (photo sequence)
Hyperion's Unusual Craters
Hyperion - Cosmic Blasting Zone

Hyperion - Cosmic Blasting Zone

http://photojournal.jpl.nasa.gov/catalog/PIA07761


This up-close view of Hyperion shows a low density body blasted by impacts over the eons. Scientists originally believed that the spongy appearance of Hyperion is caused by a phenomenon called thermal erosion, in which dark materials accumulating on crater floors are warmed by sunlight and melt deeper into the surface, allowing surrounding ice to vaporize away.
Cassini scientists now think that Hyperion's unusual appearance can be attributed to the fact that it has an unusually low density for such a large object, giving it weak surface gravity and high porosity. These characteristics help preserve the original shapes of Hyperion's craters by limiting the amount of impact ejecta coating the moon's surface. Impactors tend to make craters by compressing the surface material, rather than blasting it out. Further, Hyperion's weak gravity, and correspondingly low escape velocity, means that what little ejecta is produced has a good chance of escaping the moon altogether.
At 280 km, (174 mi) across, Hyperion's impact-shaped morphology makes it the largest of Saturn's irregularly-shaped moons.
Images were taken by the Cassini spacecraft at a distance of about 33,000 km (20,500 mi) from Hyperion. Image scale is 197 meters per pixel.
NASA/JPL/Space Science Institute