Stadium-size moonlets around Saturn, CU researchers say

Bill Scanlon, Rocky Mountain News

Published October 24, 2007 at midnight

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Moons the size of football stadiums speckle Saturn's outermost ring, likely because a comet or meteoroid broke a larger moon apart hundreds of millions of years ago, University of Colorado researchers have discovered.

CU-Boulder research associate Miodrag Sremcevic said images taken by a camera aboard the NASA Cassini spacecraft reveal eight propeller-shaped "wakes" in a thin belt of Saturn's "A" ring.

The propeller shapes indicate where the ring matter has been perturbed by the gravitational pull of the moonlets, some as big as football stadiums, some as small as semitrailers.

Sremcevic is lead author of a paper on the discovery which appears this week in the prestigious scientific journal Nature.

There are likely thousands of moonlets in the ring, Sremcevic's team concluded.

The images were taken by the Narrow Angle Camera onboard the NASA Cassini spacecraft, which was launched in 1997 and has been orbiting the Saturn system since July 2004.

Saturn's ring system is about 155,000 miles across, nearly two-thirds the distance between the Earth and its moon. The thin moonlet belt in Saturn's outermost ring is about 2,000 miles in diameter.

"This is the first evidence of a moonlet belt in any of Saturn's rings" said Sremcevic of CU-Boulder's Laboratory for Atmospheric and Space Physics.

Co-authors of the Nature study include Juergen Schmidt, Martin Seiss and Frank Spahn of the University of Potsdam in Germany, Heikko Salo of the University of Oulu in Finland, and Nicole Albers of CU-Boulder's LASP.

Sremcevic and Spahn first predicted the existence of the propellers in Saturn's rings in 2000.

CU's Larry Esposito and Joshua Colwell in 1987 first proposed that Saturn's rings were created in a "collisional cascade" of ring debris during a catastrophic break-up of an even larger moon in the Saturn system.

The newly discovered moonlets probably formed after Saturn's rings already were in place, hundreds of millions or even billions of years ago.

Esposito said the propellers "show a striking demonstration of the lingering effects of the gravity."

Esposito is the chief scientist on the NASA Cassini mission's Ultra-Violet Imaging Spectrograph that was designed and built at CU's LASP, but was not involved in the new study.

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