View of Hyperion revealing details across its surface, obtained during the space probe Cassini's flyby in Sept 2005. It is made up of a combination of images taken using infrared, green and ultraviolet spectral filters.
Credit: NASA/JPL/Space Science Institute.
PARIS: Astronomers looking at close-up pictures of Saturn's moon Hyperion, say the spud-shaped rock has a "sponge-like appearance" unlike anything ever seen before.
As much as 40 per cent of Hyperion could be porous, they report in the U.K. journal Nature.
High-resolution images of Hyperion were sent back to Earth in four flybys in 2005 and 2006 by the U.S. space probe Cassini, which in its closest pass swooped to within 618 km of its surface, getting picture resolution as fine as a few kilometres across.
"The most striking visual aspect of Hyperion is its sponge-like appearance, which is unlike any other object imaged to date," they report.
Punching holes
Hyperion is peppered with craters, most of which are between two and 10 kilometres across, and are well preserved. The apparent reason for this is that the surface is so porous, that an impacting space rock causes little ejecta – the name for material that is blasted out of the collision sites.
The moon has a mean diameter of 270 km, but its shape is so irregular that this varies between 190 and 364 kms. It is the eighth-largest and the largest irregularly-shaped satellite of the 48 named Saturnian moons.
Hyperion's strange shape may have been caused by bombardment by meteors, which blew part of its surface away, some experts believe. The new study was headed by Peter Thomas of the Centre for Radiophysics and Space Research at Cornell University in New York, USA.
In a companion paper, Dale Cruikshank of the space agency NASA's Ames Research Center and colleagues report that Hyperion's surface is relatively reflective but the bottoms of the craters are dark, similar to those found on the Saturnian moons Phoebe and Iapetus.
