Asked by: Richard O’Neill, Glasgow
It is not entirely clear why Saturn possesses rings. Astronomers have developed three theories of their formation. They could have formed from material left over from the formation of the planet itself – material that was unable to form a moon. Or, they could have formed from the debris of a moon that was destroyed by a large impact, perhaps by a comet or asteroid. Finally, they may have formed from a moon that broke apart due to the tidal forces from Saturn itself.
If the rings were formed along with the planet, then they will have had about four billion years to gather a large amount of ‘dirt’ from micrometeorite impacts. However, Saturn’s rings (composed mostly of water ice) are almost completely devoid of such ‘dirt’, implying they are actually quite young. This may suggest the impacted moon hypothesis is more likely. However, the jury is still out on this question.