Saturn's Rings as Old as Solar System, Study Says

Richard A. Lovett in San Francisco, California
for National Geographic News
December 13, 2007

Saturn's rings may be nearly as old as the solar system, a new study says, contradicting prior calculations that they clock in at only a few hundred million years.

That's because ring particles may have been repeatedly recycled during the previous four billion years, said study author Larry Esposito of the University of Colorado at Boulder—a finding that hints that the rings could last for many more eons.

Traditionally, experts have believed that Saturn's rings are the remnants of one or more small moons that broke up when they were hit by asteroids or comets.

According to the theory, additional collisions among the debris formed the fine ring particles we see today. But that couldn't have happened all that long ago, because otherwise continued meteorite bombardment would have hammered all of the particles to dust too fine to form visible rings.

Furthermore, the rings are full of features that appear to be quite young. (Related: "Moonlet Study Sheds Light on Origins of Saturn's Rings" [October 24, 2007].)

"Before, we thought that Saturn's rings had been recently created because we see many recently created features," Esposito said.

Too Young and Too Old

But scientists are obtaining ever-more-detailed observations of Saturn from NASA's orbiting Cassini spacecraft.

"The Cassini results are extending what we know about Saturn's rings in a particularly interesting way," Esposito said. "We see many even more youthful structures, not consistent with a single event that created the rings, say, in the age of the dinosaurs."

Rather, he said, "clumps," "propellers," "spokes," and other features come and go rapidly as tidal forces or collisions break them apart, while gravitational attraction causes new ones to form.

"We're seeing the rings as continuously recycling," he added. "Because of this, we can accommodate not only the dynamic, youthful processes that we see, but also the persistence of the rings. They're probably as old as the solar system and probably will last billions of years into the future."

There also appears to be about three times as much mass hiding in ring clumps than was previously suspected, Esposito said.

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