July 5, 2007 — In the family of eclectic moons circling Saturn, Hyperion stands alone, not only for its irregular shape and chaotic rotation, but because of its oddly porous surface, new research culled from the Cassini space probe shows.

"The most striking visual aspect of Hyperion is its sponge-like appearance, which is unlike that of any other object imaged to date," writes Cornell University planetary scientist Peter Thomas, lead author of a paper about Hyperion appearing in this week's issue of the journal Nature.

The eighth-largest of Saturn's brood is peppered with relatively well-preserved craters that measure between two and 10 kilometers (1.2 to 6.2 miles) in diameter.

Scientists theorize that Hyperion's spongy surface, which comprises about 40 percent of the moon by volume, limits how much debris is stirred up during impacts.

"The high porosity may be the crucial factor in crafting this unusual surface," said Thomas.