Saturn’s irregularly shaped moon Hyperion, received its last close inspection from NASA’s Cassini spacecraft, before the probe heads on to its icy neighbour Dione. Close-up images taken 31 May reveal dark material lining the floors of many craters that cover the pock marked and unusual surface of the moon, helping to uphold the suggestion that Hyperion is truly one of the oddballs meandering around the Solar System.
Hyperion, which not only looks like a giant piece of pumice, is also porous like pumice and has a low density – about half that of water – causing the moon to have a weak surface gravity. Its low density could signify that Hyperion is composed mostly of water ice and that only a small amount of rock makes up the rest of the moon. This theory is also favourable as many of Hyperion’s crater walls are bright, suggesting an abundance of water ice. With characteristics like this collisions with its surface tend to result in compression of material rather than excavation and debris that is blown from the moon does not resettle but is lost to space.
Cassini’s task of imaging Hyperion from different angles in the hope of seeing different terrain is made all the more difficult by the moon’s chaotic and somewhat unpredictable tumble around Saturn. One hypothesis for its irregular shape is that Hyperion is a remnant from a much larger body that fragmented after a collision with another object – a process that some researchers attribute to the creation of our own moon.
Prior to its final mission, set for 2017, Cassini will continue to make several more flybys of Saturn’s moons. Cassini’s grand finale will see the spacecraft repeatedly dive through the space between Saturn and its rings, after a year-long mission to prepare it for this daring final act.