杏吧原创

WHY are Saturn鈥檚 rings so spectacular? It could be that the planet managed to cling onto a moon when all the other gas giants in our solar system had already lost theirs. Today鈥檚 rings formed when the moon was smashed up.

and colleagues at the University of Diderot, Paris, suggest it was during the 鈥渓ate heavy bombardment鈥�, 700 million years after Saturn formed, that a chunk of debris collided with one of the planet鈥檚 moons. Because the moon was orbiting at just the right distance from Saturn when it shattered 鈥� within the so-called Roche limit 鈥� the tiny pieces formed the rings instead of dispersing.

This could explain why other planets don鈥檛 have rings like Saturn鈥檚. Even if other planets had moons within their Roche limits at the birth of the solar system, the team鈥檚 calculations show that the moons would soon been dragged down into the planet or unshackled from their orbits. Yet Saturn鈥檚 rapid rotation meant it could hold a satellite within its Roche limit until the bombardment. will appear in the journal Icarus.

from the Institute of Astronomy in Edinburgh, UK, says the team鈥檚 way of showing Saturn鈥檚 uniqueness among gas giants is interesting, but that their hypothesis cannot be proved until we have better ways of modelling the evolution of the solar system.

Cassini: Mission to Saturn 鈥� Learn more in our continually updated .