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Wednesday, September 24, 2008

New Thinking: Saturn's Rings Might Be Ancient

By Clara Moskowitz
Staff Writer

Saturn's rings may be much older and more massive than previously thought, according to a new study.

The study's computer simulation showed how the planet's rings could date back billions of years ago to the early ages of the solar system, rather than only 100 million years ago (during Earth's Age of Dinosaurs), as previous observations suggested. The calculations are consistent with recent observations of the rings by the Cassini–Huygens spacecraft currently studying Saturn and its moons.

Larry Esposito and Joshua Elliott, both at the University of Colorado, modeled how meteorites smash into the rings, shattering the ring particles and coating each one in a layer of ice and dust. Before, scientists had assumed that this shattering led to the eventual dissipation of the rings, but a new simulation, created by Glen Stewart and Stuart Robbins of the University of Colorado, shows that after breaking up, the particles could again clump together in a perpetual recycling process.

Previously, researchers had thought the rings were relatively young because they appeared bright and pristine, not covered with the detritus of billions of years of meteorites smashing into them. But the new calculations show that if the effect of this clumping and re-clumping is taken into account, the dust would also be recycled through the rings and wouldn't appear as dark as might be expected.

Many scientists had assumed that we just happened to be catching Saturn at a relatively rare time when it had rings. Now it would seem Saturn, and maybe lots of other large planets in the universe also, could have rings for much of their lives.

"Both Cassini observations and theoretical calculations can allow the rings of Saturn to be billions of years old," said Esposito, principal investigator of Cassini's Ultraviolet Imaging Spectrograph (UVIS) instrument. "This means we humans are not just lucky to see rings around Saturn. This would lead us to expect massive rings also to surround giant planets circling other stars."

Our own Jupiter, Uranus and Neptune each have rings, and even Earth might have had them once.

Earlier estimates of Saturn's rings' mass had come from observations of how much starlight is blocked by the rings. But the new calculations indicate that these measurements underestimate the mass by about a factor of three, since they do not account for the clumping effect.

If the rings are really more massive than thought, that could also help explain why the rings appear so bright and clean. The more individual pieces of mass in the rings, the more material there is to spread the pollution around, so the less noticeable it would be to outside observations.

Esposito will present these findings at the European Planetary Science Congress in Muenster, Germany, on Sept. 23. Cassini–Huygens is a joint project by NASA, the European Space Agency, and Italian Space Agency.