[meteorite-list] Saturn's Rings May be Old Timers

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 19 Dec 2007 13:41:27 -0800 (PST)
Message-ID: <200712192141.NAA11235_at_zagami.jpl.nasa.gov>


Saturn's Rings May be Old Timers
Jet Propulsion Laboratory
December 12, 2007

SAN FRANCISCO, Calif. - New observations by NASA's Cassini spacecraft
indicate the rings of Saturn, once thought to have formed during the age
of the dinosaurs, instead may have been created roughly 4.5 billion
years ago, when the solar system was still under construction.

Larry Esposito, principal investigator for Cassini's Ultraviolet Imaging
Spectrograph at the University of Colorado, Boulder, said data from
NASA's Voyager spacecraft in the 1970s, and later from NASA's Hubble
Space Telescope, led scientists to believe Saturn's rings were
relatively youthful and likely created by a comet that shattered a large
moon, perhaps 100 million years ago.

But ring features seen by instruments on Cassini -- which arrived at
Saturn in 2004 -- indicate the rings were not formed by a single
cataclysmic event. The ages of the different rings appear to vary
significantly, and the ring material is continually being recycled,
Esposito said.

"The evidence is consistent with the picture that Saturn has had rings
all through its history," said Esposito of the University of Colorado's
Laboratory for Atmospheric and Space Physics. "We see extensive, rapid
recycling of ring material, in which moons are continually shattered
into ring particles, which then gather together and re-form moons."

Esposito and colleague Miodrag Sremcevic, also with the University of
Colorado, are presenting these findings today in a news briefing at the
meeting of the American Geophysical Union in San Francisco.

"We have discovered that the rings probably were not created just
yesterday in cosmic time, and in this scenario, it is not just luck that
we are seeing planetary rings now," said Esposito. "They probably were
always around but continually changing, and they will be around for many
billions of years."

Scientists had previously believed rings as old as Saturn itself should
be darker due to ongoing pollution by the "infall" of meteoric dust,
leaving telltale spectral signatures, Esposito said. But the new Cassini
observations indicate the churning mass of ice and rock within Saturn's
gigantic ring system is likely much larger than previously estimated.
This helps explain why the rings overall appear relatively bright to
ground-based telescopes and spacecraft.

"The more mass there is in the rings, the more raw material there is for
recycling, which essentially spreads this cosmic pollution around," he
said. "If this pollution is being shared by a much larger volume of ring
material, it becomes diluted and helps explain why the rings appear
brighter and more pristine than we expected."

Esposito, who discovered Saturn's faint F ring in 1979 using data from
NASA's Pioneer 11 spacecraft, said a paper by him and his colleagues
appearing in an upcoming issue of the journal Icarus supports the theory
that Saturn's ring material is being continually recycled. Observing the
flickering of starlight passing through the rings in a process known as
stellar occultation, the researchers discovered 13 objects in the F ring
ranging in size from 27 meters to 10 kilometers (30 yards to six miles)

Since most of the objects were translucent -- indicating at least some
starlight was passing through them -- the researchers concluded they
probably are temporary clumps of icy boulders that are continually
collecting and disbanding due to the competing processes of shattering
and coming together again. The team tagged the clumpy moonlets with cat
names like "Mittens" and "Fluffy" because they appear to come and go
unexpectedly over time and have multiple lives, said Esposito.

Esposito stressed that Saturn's rings of the future won't be the same
rings we see today, likening them to great cities around the world like
San Francisco, Berlin or Beijing. "While the cities themselves will go
on for centuries or millennia, the faces of people on the streets will
always be changing due to continual birth and aging of new citizens."

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

For more information about the Cassini-Huygens mission, visit:
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini . To listen
to a podcast of Esposito and view a short video animation of objects in
Saturn's F ring shattering and re-forming, visit:


Media Contact: Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
carolina.martinez at jpl.nasa.gov

Jim Scott 303-492-3114
University of Colorado, Boulder
jim.scott at colorado.edu

Received on Wed 19 Dec 2007 04:41:27 PM PST

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