Explanation: What lies at the bottom of Hyperion 's strange craters? Nobody's sure . To help find out, the robot Cassini spacecraft now orbiting Saturn swooped past the sponge-textured moon in 2005 and 2010 and took images of unprecedented detail. An image from the 2005 pass, shown above in false color, shows a remarkable world strewn with strange craters and a generally odd surface . The slight differences in color likely show differences in surface composition. At the bottom of most craters lies some type of unknown dark material . Inspection of the image shows bright features indicating that the dark material might be only tens of meters thick in some places. Hyperion is about 250 kilometers across, rotates chaotically , and has a density so low that it might house a vast system of caverns inside.