Saturn's rings may double up as a moon factory

Space 30 November 2012
Spawn of the rings, perhaps




The rings mark Saturn’s Roche limit: the distance from the planet beyond which its gravitational tidal forces are weak enough to let moons there survive. Inside the Roche limit, however, Saturn’s gravity would pull moons apart and add them to its rings. Some astronomers think this is how the planet gained its rings in the first place.





Smoking gun

Neither Uranus nor Neptune has a massive ring system today, but the distribution of moons around both planets is similar enough to the Saturn pattern to suggest that they once did – and that the rings gave rise to both of the ice giants’ satellites. “We think this is a smoking gun of this process,” Crida says. Uranus and Neptune clearly lack big rings today, though, so we would need a better understanding of the ring-forming process to establish whether they might have done in the past.

Surprisingly, even the Earth could have had a ring once. Earth’s moon probably formed when a large body collided with the young planet and sent hot mantle material flying into space.

“The process through which this material would eventually form the moon was not investigated in detail so far,” Crida says. If the material settled into a massive ring, it could have spread and congealed into a single moon in as little time as a month, he says.

Journal: Science,

More on these topics: