Cassini pictures spongy Hyperion

Another spectactular picture from this hugely successful mission(Nasa/JPL/SSI) Enlarge Image

It may have the look of a giant sponge, but this is Saturn's moon Hyperion, as pictured by the Cassini spacecraft.

The US-European probe has just made a flyby of the satellite, crossing its surface at a distance of just 500km.

The surface is speckled with impact craters which scientists say have been modified by some process, not yet understood, to create the strange look.

Much of the interior of Hyperion is empty space, suggesting it is little more than a pile of space rubble.

Researchers say they are keen to learn the nature of the dark material which seems to cover the floor of some craters.

Also in Cassini's sights recently has been the moon Tethys. It is much bigger.

Tethys is set for another close inspection in 2007 (Nasa/JPL/SSI) Enlarge Image

Whereas Hyperion is just 266km across, Tethys has a diameter of 1,071km.

Clearly visible in the new picture is the giant scar dubbed Ithaca Chasma. It is about 65km wide and several km deep.

Cassini will return to Tethys in 2007 for another close look. Another flyby of Hyperion is not scheduled in the initial four-year mission to the Saturnian system.

The $3.2bn Cassini-Huygens project is a joint venture between the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).