The moon that is 40% empty space

Saturn's moon Hyperion has been described by scientists as a "fluffy snowball". Saturn's moon was closely monitored by the Cassini spacecraft that flew closer to Saturn late last year. The spacecraft found that there was a high proportion of craters which has created a irregular appearance which scientists have described as a "fluffy snowball". On board the Cassini spacecraft they have different types of cameras which they used to discover a network of underground tunnels full of empty space which is what makes the Hyperion moon 40% empty space. 

Saturn's moon Hyperion is a jumble of icy rubble (Image: NASA/JPL/Space Science Institute)