Saturn System Driven By Ice, Says CU-Boulder Researcher

http://www.colorado.edu/news/releases/2004/403.html

University of Colorado at Boulder
News Release

Saturn System Driven By Ice, Says CU-Boulder Researcher
Dec. 16, 2004

Ice particles are key players in the ever-changing panorama at Saturn,
according to a new study led by a University of Colorado at Boulder
professor using an instrument on the Cassini-Huygens spacecraft now at
the ringed planet.

Larry Esposito of the Laboratory for Atmospheric and Space Physics said
data from the Ultraviolet Imaging Spectrometer, or UVIS, indicates much
of Saturn's system is filled with ice, as well as atoms derived from
water. Esposito is the principal investigator for the $12.5 million
UVIS
instrument riding on the craft.

Esposito said hydrogen and oxygen atoms are widely distributed in the
planetary system, which extends millions of miles outward from Saturn.
Cassini researchers are seeing large fluctuations in the amount of
oxygen in the Saturn system, he said.

"A possible explanation for the fluctuation in oxygen is that small,
unseen icy moons have been colliding with Saturn's E ring," said
Esposito. "The collisions may have produced small grains of ice, which
yielded oxygen atoms when struck by energetic, charged particles in
Saturn's magnetosphere. UVIS is able to identify these glowing atoms."

A paper on the subject authored by Esposito and colleagues appears in
the Dec. 16 issue of Science Express, the online version of Science
magazine. Esposito also will give a presentation on the new results
from
the Cassini-Huygens mission at the Fall Meeting of the American
Geophysical Union, being held this week through Friday in San
Francisco.

Saturn's ring particles may have formed originally from pure ice,
Esposito said. But they have since been subjected to continual
bombardment by meteorites, which has contaminated the ice and caused
the
rings to darken.

Over time, incessant meteorite bombardment has likely spread the dirty
material resulting from the collisions widely among the ring particles,
he said. But instead of uniformly dark rings, the UVIS instrument is
recording "radial variations" that show brighter and darker bands in
the
individual rings.

"The evidence indicates that in the last 10 million to 100 million
years, fresh material probably was added to the ring system," he said.
The research team proposed that such "renewal events" are from the
fragmentation of small moons, each probably about 20 kilometers (12
miles) across.

"The interiors of the tiny moonlets, which have been shielded from
contamination by the continual collisions with each other, are the
source of purer water ice," he said. "Both the oxygen fluctuation and
the spectral variation in Saturn's rings support a model of ring
history
in which small moons are continually destroyed to produce new rings."

The ice grains released by the continual moonlet collisions are bathed
by Saturn's radiation belt, liberating the oxygen atoms that are seen
by
UVIS in the ultraviolet as they reflect sunlight in the immense cloud
surrounding Saturn, said Esposito.

Other authors on the Science Express paper include LASP's Joshua
Colwell, Kristopher Larsen, William McClintock and Ian Stewart.
Researchers from the University of Southern California, NASA's Jet
Propulsion Laboratory, Central Arizona University, the California
Institute of Technology and the Max Planck Institute and Stuttgart
University in Germany also co-authored the paper.

Launched in 1997, the Cassini-Huygens spacecraft achieved Saturn orbit
June 30. During the spacecraft's four-year tour of the Saturn system,
the UVIS team will continue to track the dynamic interactions of the
planet's rings, moons and radiation belts, Esposito 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, Calif., manages the Cassini-Huygens mission for NASA's
Science
Mission Directorate in Washington, D.C.

Contact: Larry Esposito, (303) 492-5990


Jim Scott, (303) 492-3114