Esa has released an image of one of Saturn 's outer moons , Hyperion . Its bubbly appearance is due to it having a very low density for its size . Scientists believe 40 per cent of the moon is made up of empty space . Comment:
Esa has released an image of one of Saturn 's outer moons , Hyperion . Its bubbly appearance is due to it having a very low density for its size . Scientists believe 40 per cent of the moon is made up of empty space . Hyperion has been known to unleash huge bursts of charged particles .