Where Saturn's Rings Came From

Saturn's rings may have originated from a satellite that was stripped of its surface ice when it moved perilously close to the planet...

Despite being one of the most iconic structures in the solar system, Saturn's rings have nonetheless defied the efforts of astronomers trying to explain their origins, largely owing to their peculiar composition - the rings are 90 to 95 per cent water ice. Previous theories have been based mainly on the destruction of a satellite through, for instance, a meteor collision; but if this were the case then the rings should contain mainly silicates, which make up the core of rocky moons. Now a new scientific model might have finally solved this circular argument.

Writing in Nature, Robin Canup of the Southwest Research Institute in Colorado has proposed that when the planet first formed about 4.5 billion years ago, there were originally several large satellites (moons) orbiting Saturn. One of these moons subsequently migrated in towards the planet, experiencing in the process intense gravitational tidal forces sufficient to strip off its icy outer layers. The liberated material then, Canup suggests, gave rise to the rings whilst the more silicate-rich centre would have fallen into Saturn itself.

Computational calculations have confirmed that this theory does, quite literally, hold water. Canup used a technique called smooth particle hydrodynamics - a computational method that can simulate fluid flows - to investigate the tidal forces exerted by Saturn on bodies orbiting close to the gas giant. 

The theory also predicts that when they first formed the rings would have been at least a thousand times more massive than they are today. But their more diminutive modern-day appearance can be explained by the presence of a number of small icy moons that are found within the rings and could have accreted material over time. In support of this suggestion, recent observations from the Cassini mission have found that accretion processes are still happening on the outer edges of the ring system, and on the satellites Pan and Atlas.