Demise of large satellite may have led to the formation of Saturn's rings and inner moons

December 12, 2010
Saturn. Photo by: NASA

Simulations performed at Southwest Research Institute may explain how Saturn's majestic rings and icy inner moons formed following the collision of a Titan-sized satellite with the planet, according to a paper published in Nature magazine's Dec. 12 Advance Online Publication.

Saturn's rings are at present 90 to 95 percent . Because dust and debris from rocky meteoroids have polluted the rings, the rings are believed to have consisted of pure ice when they formed. This composition is unusual compared to the approximately half-ice and half-rock mixture expected for materials in the outer Solar System. Similarly, the low densities of Saturn's inner moons show that they too are, as a group, unusually rich in ice.

The previous leading ring origin theory suggests the rings formed when a small satellite was disrupted by an impacting . "This scenario would have likely resulted in rings that were a mixture of rock and ice, rather than the ice-rich rings we see today," says the paper's author, Dr. Robin M. Canup, associate vice president of the SwRI Directorate in Boulder.

The new theory links the formation of the rings to the formation of Saturn's satellites. While Jupiter has four large satellites, Saturn has only one, Titan. Previous work suggests that multiple Titan-sized satellites originally formed at Saturn, but that those orbiting interior to Titan were lost as their orbits spiraled into the planet.

Demise of large satellite may have led to the formation of Saturn's rings and inner moons
At the end of the formation of Saturn’s satellites, a Titan-sized satellite spirals inward toward the planet due to interaction with the primordial circumplanetary gas disk. As the satellite approaches the planet’s surface, planetary tides strip material from its outer icy layers, producing material that eventually forms a massive ice ring. Here, a smooth particle hydrodynamics (SPH) simulation, in which matter is represented as particles, is used to model tidal stripping from a Titan-sized satellite consisting of 45 percent ice in an outer mantle and 55 percent silicate and metal in an inner core. The frames show material stripped from the satellite after [left] 8 simulated hours and [right] 25 simulated hours, assuming a fixed satellite orbit indicated by the outer dashed circle. On a much longer timescale, the satellite’s orbital radius slowly decreases, with tides continuing to strip off ice until the satellite’s rocky core collides with the planet. The inner dashed circle indicates Saturn’s current mean radius, RS. Saturn’s surface at the time of ring formation was larger than this, probably at about 1.5RS. Image courtesy of Southwest Research Institute

As the final lost satellite neared , heating caused by the flexing of its shape by the planet's gravity would cause its ice to melt and its rock to sink to its center. Canup uses numerical simulations to show that as such a satellite crosses the region of the current B ring, planetary tidal forces strip material from its outer icy layers, while its rocky core remains intact and eventually collides with the planet. This produces an initial ice ring that is much more massive than Saturn's current rings.

Over time, collisions in the ring cause it to spread radially and decrease in mass. Inwardly spreading ring material is lost, while material spreading past the ring's outer edge accumulates into icy moons with estimated masses consistent with the inner moons seen today.

"The new model proposes that the rings are primordial, formed from the same events that left Titan as Saturn's sole large satellite, " says Canup. "The implication is that the rings and the Saturnian moons interior to and including Tethys share a coupled origin, and are the last remnants of a lost companion to Titan."

During its extended mission, the Cassini spacecraft will measure the rings' current mass and will indirectly measure the pollution rate of the rings. This should provide an improved estimate of the rings' age and a test of the new ring origin model.

Explore further: Cassini Finds Possible Origin of One of Saturn's Rings

More information: The paper, "Origin of Saturn's Rings and Inner Moons by Mass Removal from a Lost Titan-Sized Satellite," by Dr. R.M. Canup, was published in Nature magazine's Dec. 12 Advance Online Publication.

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1.5 / 5 (14) Dec 12, 2010

Old programming adage applies.
Garbage in garbage out.

This is nothing but wild speculation.

In the computer you can apply whatever rules you want and then modify them anyway you want to get your desired result.

You can even make pigs fly at the speed of light.

But first take a big tab of acid and whammo, I just figured out how the rings of Saturn formed on my pc. Let pubish a paper guys.
1 / 5 (10) Dec 12, 2010
Saturn molecules everything of moonspeed but anything on lightplanets. To be read at my website and already liked by American Phycicist, Facebook.
1 / 5 (10) Dec 12, 2010
Mean, moonspeed (rings) relative lightplanets (moons). That's why 'they' called it Sa-turn because whe don't like to remember 'it' as sat-Urn, Albert.
1 / 5 (2) Dec 12, 2010
I prefer the notion that dues to Saturn's gravity squeezing the moon Enceladus... it's spewing out ice volcanoes... which in turn the plumes are collecting to form the rings of Saturn which slowly spiral inwards.
1 / 5 (8) Dec 13, 2010
Having difficulty to explain the origin?

The researchers will have an incredibly difficult time to reconcile their pollution findings with the expected age when they get the results back.

Just as an aside - what age are they expecting for the rings, exactly? Surely they should use some kind of theory and make a prediction, not try and fit the results into a framework afterwards?

Seeing that the rings seem to consist mostly of water/ice, it is inconceivable that they should have been around for more than 1m years at best. So the researchers are onto a hiding when the pollution results show an age less then 4 billion years.
1 / 5 (5) Dec 13, 2010
As a computer scientist and having a fetish for science.
I agree 500% with A2G.
not rated yet Dec 13, 2010
If somthing occurs naturally is it pollution
5 / 5 (2) Dec 13, 2010
... not try and fit the results into a framework afterwards?

Pot,kettle,black. It's amazing you state that the universe is so young when you don't have any evidence for that. At best, you have a gap where scientists are currently puzzled. You then want to claim victory and state that the universe is much younger. What if we actually adopted that position? At what cost? Momentarily solving a handful of problems that may be explained by a young universe, whilst simultaneously creating a million more problems that were solved with our current model? The fact is, accepting a young universe solves a few problems but causes many many more. We're better off with our current model. Why would you want to back pedal?

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