[meteorite-list] New Cassini Image At Saturn Shows 'A' Ring Contains More Debris Than Once Believed

[Ron Baalke]

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

Contact:
Joshua Colwell, (303) 492-6805
Larry Esposito, (303) 492-5990
Jim Scott, (303) 492-3114

April 6, 2006

New Cassini Image At Saturn Shows 'A' Ring Contains More Debris Than Once 
Believed

Views of Saturn's stunning ring system from above by the Cassini-Huygens 
spacecraft now orbiting the planet indicate the prominent A ring contains 
more debris than once thought, according to a new University of Colorado 
at Boulder study.

Previous observations with the Voyager spacecraft in the early 1980s found 
the ring was more transparent, indicating less material, said Joshua 
Colwell of CU-Boulder's Laboratory for Atmospheric and Space Physics. But 
new calculations based on May 2005 observations with Cassini's Ultraviolet 
Imaging Spectrograph, or UVIS, indicates the opacity of the ring is up to 
35 percent higher than previously reported.

Because of the uneven distribution of the ring particles -- which range in 
size from dust grains to school buses -- the transparency of the rings 
depends on the angle from which they are viewed, he said. The particles 
are arranged essentially parallel in long stringy clumps as large as 60 
feet across, 16 feet thick and 160 feet long, according to models produced 
from observation data, said Colwell.

A paper on the subject by Colwell, Larry Esposito and Miodrag Sremcevic of 
CU-Boulder's LASP appears in the April 1 issue of Geophysical Research 
Letters, or GRL. Esposito is science team leader for UVIS, a $12.5 million 
instrument designed and built at CU-Boulder by LASP that is riding on the 
Cassini spacecraft.

A new image released by the team in conjunction with the GRL paper shows 
the distribution of the ring material. The opaque B ring has more material 
than the A ring, located just outside it, and the A ring is densest near 
its inner edge, according to the team. The new clumps observed by Cassini 
mean a larger amount of material overall said Colwell, a LASP research 
associate and UVIS science team member.

The particles are trapped in ever-changing clusters of debris that are 
regularly torn apart and reassembled by gravitational forces from the 
planet, Colwell said. The size and behavior of the clusters were deduced 
by observing flickering light as the ring passed in front of a star in a 
process known as stellar occultation, he said.

"The flickers are like a time-lapse movie of a car's headlights taken from 
the other side of a picket fence," said Colwell. "The flickering would 
provide us details about the pickets."

The observations of the particle clusters indicate the A ring is primarily 
empty space. A close-up view of the rings would show as "short, flattened 
strands of spiral arms with very few particles between them," he said.

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 Cassini-Huygens mission for NASA's Science Mission Directorate in 
Washington, D.C.

The Cassini orbiter was designed, developed and assembled at JPL. For more 
information about the Cassini-Huygens mission, visit
     http://saturn.jpl.nasa.gov
The ultraviolet imaging spectrograph team home page is at
     http://lasp.colorado.edu/cassini

[NOTE: An image supporting this release is available at
http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2074 ]