Death Star moon may be ‘wonky or watery’ 10-16-2014 | Jonathan Webb, Science reporter, BBC News
Mimas is nicknamed the Death Star because it resembles the infamous Star Wars space station.
It has a tell-tale wobble that is twice as big as expected for a moon with a regular, solid structure.
The researchers offer two explanations: either it has a vast ocean beneath its surface, or a rocky core with a weird shape resembling a rugby ball.
The study appears in Science Magazine.
Its authors are astronomers in the US, France and Belgium, who based their calculations on high-resolution photos of Mimas snapped by the Cassini spacecraft.
Cassini was sent to Saturn in 1997 to explore the planet and its many moons, which so far number 62 (53 with names).