London, Oct 13 : A new study has suggested that Saturn's rings may be remains of an ancient moon that shattered because of a collision with a chunk of debris 700 million years ago.
Sebastien Charnoz and colleagues at the University of Diderot, Paris, suggest that it was during the "late heavy bombardment", 700 million years after Saturn formed, that a chunk of debris collided with one of the planet's moons.
According to a report in New Scientist, because the moon was orbiting at just the right distance from Saturn when it shattered - within the so-called Roche limit - the tiny pieces formed the rings instead of dispersing.
This could explain why other planets don't have rings like Saturn's.
Even if other planets had moons within their Roche limits at the birth of the solar system, the team's calculations show that the moons would soon been dragged down into the planet or unshackled from their orbits.
Yet, Saturn's rapid rotation meant it could hold a satellite within its Roche limit until the bombardment.
According to Ken Rice from the Institute of Astronomy in Edinburgh, UK, the team's way of showing Saturn's 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.