Recycled youth: An artist concept of a close-up view of Saturn's ring particles. Saturn is seen in the background (yellow and brown). The particles (blue) are composed mostly of ice, but are not uniform. They clump together to form elongated, curved aggregates, continually forming and dispersing. The space between the clumps is mostly empty. The largest individual particles shown are a few meters (yards) across.

Credit: NASA/JPL/University of Colorado

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NEW YORK: Once thought to have been born during the age of the dinosaurs, Saturn's rings might instead be far more ancient and sustained by the recycling of rock and ice, says a new study.

"Saturn's rings could have lasted as long as the Solar System and maybe will be around for billions of years," said Larry Esposito, a planetary scientist at the University of Colorado in Boulder and principal investigator for the Ultraviolet Imaging Spectrograph on NASA's Cassini spacecraft.

Stray comet

Based on previous observations by NASA's Voyager probes and the Hubble Space Telescope, scientists had thought that the gas giant's rings were created when a stray comet collided with one of Saturn's moon about 100 million years ago.

But new analyses of Cassini data by Esposito's team, indicate the rings contain much more material than previously realised, which could dramatically change estimates of their age. The findings were presented today at the annual meeting of the American Geophysical Union, held in San Francisco.

Scientists once thought that if Saturn's rings were ancient, they should be darker due to ongoing pollution by the "infall" of meteoric dust. Models predict, however, that the more rock and ice Saturn's rings contain, the less darkening will occur.

"If this pollution is being shared by a much larger volume of ring material, it becomes diluted and helps explain why the rings appear brighter and more pristine than we expected," Esposito said.

Clumping moonlets

He and his team agree that Saturn's rings were likely first formed from the fragments of a shattered moon, but they think the cataclysmic event occurred as long as 4.5 billion years ago, during the Solar System's youth, and that the rings have survived to this day because of constant recycling.

Under this scenario, Saturn's ring particles are constantly clumping to form small "moonlets," which in turn are continually colliding with one another and shattering to create new particles. Esposito said his team has found evidence of 13 transient moonlets in Saturn's F-ring, which they will detail in an upcoming issue of the journal Icarus.

If the rings are constantly being recycled, then they are constantly changing, and the rings we see today will not be the same ones that girdle Saturn in the future, Esposito said.

He compares the rings to great cities around the world like San Francisco, Berlin or Beijing. "While the cities themselves will go on for centuries or millennia, the faces of people on the streets will always be changing due to continual birth and aging of new citizens."