[meteorite-list] New Study Confirms First-Known Belt Of Moonlets In Saturn Rings

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 24 Oct 2007 14:40:04 -0700 (PDT)
Message-ID: <200710242140.OAA10565_at_zagami.jpl.nasa.gov>

http://www.colorado.edu/news/releases/2007/411.html

Office of News Services
University of Colorado-Boulder
Boulder, Colorado

Contact:
Miodrag Sremcevic, (303) 492-3395
Nicole Albers, (303) 735-4459

Oct. 24, 2007

New CU-Boulder Study Confirms First-Known Belt Of Moonlets In Saturn Rings

A narrow belt harboring moonlets as large as football stadiums discovered in
Saturn's outermost ring probably resulted when a larger moon was shattered
by a wayward asteroid or comet eons ago, according to a University of
Colorado at Boulder study.

Images taken by a camera onboard the NASA Cassini spacecraft revealed a
series of eight propeller-shaped "wakes" in a thin belt of the outermost "A"
ring, indicating the presence of corresponding moonlets, said CU-Boulder
Research Associate Miodrag Sremcevic, lead author of the study published in
the Oct. 25 issue of Nature. The propeller wakes highlight tiny areas of the
belt where ring material has been perturbed by the gravitational forces
caused by individual moonlets, Sremcevic said.

The team calculated that there likely are thousands of moonlets ranging in
size from semi-trailers to sports arenas embedded in the "A" ring's thin
moonlet belt that circles the planet. At about 2,000 miles across, the belt
of moonlets is only about 1/80th the diameter of Saturn's total ring system,
which at roughly 155,000 miles across would stretch about two-thirds of the
way from Earth to the moon.

"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.
"We have firmly established these moonlets exist in a relatively narrow
region of the "A" ring, and the evidence indicates they are remnants of a
larger moon that was shattered by a meteoroid or comet."

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. 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.

Each propeller feature is about 10 miles long, said Sremcevic, who with
Spahn first predicted the existence of such propellers in Saturn's rings as
an undergraduate at the University of Belgrade in 2000. While four
propellers were discovered in the "A" ring in 2006 by a team led by Cornell
University, Sremcevic and his colleagues looked at a much larger image
sequence, allowing them to extrapolate statistically and confirm the
presence of thousands of small objects in the "A" ring's moonlet belt.

The moonlets may be the result of the break-up of a ring-moon similar to Pan
-- Saturn's innermost 20-mile diameter moon -- that was smashed by a comet
or meteor, the team concluded. The team calculated the mass of the unseen
moonlets in the belt greater than 50 feet in diameter to arrive at the
estimated size of the moon involved in the collision creating the belt.

The finding supports the theory that Saturn's rings initially were created
in a "collisional cascade" of ring debris begun by a catastrophic break-up
of an even larger moon in the Saturn system first proposed by CU-Boulder
planetary scientists Larry Esposito and Joshua Colwell in 1987. The moonlets
in the newly discovered belt may have formed after Saturn's rings already
were in place, which planetary scientists speculate could have been hundreds
of millions or even billions of years ago.

"It seems unlikely that moonlets are remainders of a single catastrophic
event that created the whole ring system, because in this case a uniform
distribution would emerge," the researchers wrote in Nature. "Instead, the
moonlet belt is compatible with a more recent body orbiting in the A ring."

Esposito, who was not involved in the study, said the propellers "show a
striking demonstration of the lingering effects of the gravity from these
small, embedded moonlets." Esposito is the chief scientist on the NASA
Cassini mission's $12.5 million Ultra-Violet Imaging Spectrograph designed
and built at LASP.

Sremcevic said the discovery of the moonlet belt is another piece in the
puzzle regarding the formation and evolution of Saturn's rings. "We believe
future studies of ring evolution will need to incorporate the findings and
implications from this study."

The NASA Cassini mission, formerly called the Cassini-Huygens mission, is a
cooperative project of NASA, the European Space Agency and the Italian Space
Agency. The Jet Propulsion Laboratory, a division of the California
Institute of Technology in Pasadena, manages the NASA Cassini mission for
NASA's Science Mission Directorate in Washington, D.C.

For more information about NASA Cassini-Huygens visit
     http://saturn.jpl.nasa.gov
To listen to a podcast of Sremcevic describing his findings visit:
     http://www.colorado.edu/news/podcasts/

IMAGE CAPTION:
[http://www.colorado.edu/news/releases/2007/images/411.jpg (56KB)]
A team led by the University of Colorado at Boulder has detected an unseen
belt of moonlets in Saturn's outermost "A" ring (top image, outer purple
band). The moonlets in the belt were detected by gravity "wakes" 10 miles to
20 miles across (boxed in bottom image) by the narrow-angle camera aboard
the NASA Cassini spacecraft. Image courtesy NASA/JPL/Space Science
Institute/University of Colorado.
Received on Wed 24 Oct 2007 05:40:04 PM PDT