How did Saturn get its rings?
Imagine two ring particles – little chunks of ice – in contact with each other near Saturn. The planet’s gravitational attraction is a little stronger on the particle closer to Saturn. This difference is called a tidal force, and is closely related to the tides in the oceans. Because of tidal forces, it’s difficult or impossible for a moon to form very close to a planet.
Saturn’s rings are probably the remnants of a large icy body that formed elsewhere and was ripped apart when it came too close to Saturn. In one scenario, a moon like Titan spiralled in through the disc of gas and dust that surrounded the young Saturn. The moon’s icy shell could have been torn off, with the fragments going into orbit around Saturn and the moon’s rocky core being swallowed by the planet. The icy chunks would have collided and spread, with the particles close to Saturn becoming the ring system and those that moved farther out coagulating into moons. In another model, a large centaur – a body that escaped the Kuiper Belt – was torn apart by Saturn’s tidal forces during a chance, very close passage. In a third concept, a moon of Saturn was destroyed by a comet impact. As in the first model, the fragments in these scenarios would have collided and formed rings and moons. Though the Cassini orbiter vastly expanded our understanding of Saturn’s rings, we still don’t know which
of these ideas is correct.