Science News

Where Saturn's Rings Came From

Sun, 12th Dec 2010

Saturnís 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.Saturn from Cassini Orbiter

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.


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I thought I had read about a "cosmic collision" theory too, as well as theory of accretion of material potentially dating back to the formation of Saturn and the solar system.

The "tidal" theory would be unlikely to explain the apparent ring-like material extending far beyond the planet and the recently discovered Phoebe ring.
CliffordK, Mon, 13th Dec 2010

There is a new theory that they were created when one of Saturn's previous moons went into a "death spiral" that ripped all the ice off the moon. At that time, there was a ring of hydrogen around Saturn that trapped the moon in Saturn's gravity. Geezer, Mon, 13th Dec 2010

Hi Geezer - maybe read the link at the top... chris, Mon, 13th Dec 2010

They don't call me "Master of the Obvious" for nothing you know. Geezer, Mon, 13th Dec 2010

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