May 31 saw NASA'sCassini spacecraft make its last close up pass with Saturn's moonHyperion. The moon has a fascinating, almost spongy appearance due tothe fact that its surface is actually less dense thanwater.
Because of Hyperion's low surface density, any collisions simply compress the surfaceinstead of excavating it. Therefore the moon is given a porousappearance rather than being pockmarked by the impact craters that sooften characterize other moons throughout the solar system.
Hyperion is the largestof Saturn's irregularly shaped moons, with a diameter of roughly 270km (168 miles). The moon had been visited by Cassini once before inSeptember 2005 when it made a much closer pass – a mere 505 km (314miles) away from the unusual celestial body.
Then, and now, imagingHyperion is essentially a game of chance. Unlike Saturn's largermoons, Hyperion tumbles unpredictably as it orbits the ringed giant,making it very difficult to predict what parts of the moon are likelyto be photographed during a pass.
The most recent, andfinal, pass saw Cassini observe Hyperion from a distance of 34,000 km(21,000 miles). During the encounter, the probe's camera snappednumerous images of the moon, that were transmitted and received backon Earth the following day.
Source: NASA
