Saturn's Spongy Moon a Quirky Satellite
What looks like a close-up of a sea sponge is actually Hyperion, a moon of Saturn that tumbles around the ringed planet at a distance of over 920,000 miles — almost four times the distance our own moon is from us!
The image above is a color-composite made from raw images taken by the Cassini spacecraft on Nov. 28, 2010, when it passed by the moon at a distance of 45,442 miles.
At right is a newer image acquired by Cassini on Sept. 16, 2011, from a distance of about 55,000 miles.
At 255 x 163 x 137 miles in diameter Hyperion is the largest of Saturn's irregularly-shaped moons and the largest irregularly-shaped moon in the solar system.
Astronomers have suggested that it's the leftovers of a larger body that was blown apart by an impact. Hyperion's sponge-like appearance may be the result of the moon's low density and high porosity, which could cause impactors to compress the surface inwards rather than blasting material out.
Unlike most of Saturn's other moons, Hyperion is not tidally locked — that is, it does not always face the same side to Saturn (like our moon does with Earth.) Rather it tumbles along in its orbit. This has prevented astronomers from thus far calculating a standard longitude-latitude map for Hyperion.
However it was formed, Hyperion sure makes for a fascinating photo subject for Cassini.