[meteorite-list] Cassini Reveals New Details About Saturn's Rings

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Sep 6 16:34:06 2005
Message-ID: <200509062032.j86KWjG12988_at_zagami.jpl.nasa.gov>

http://www.pparc.ac.uk/Nw/dps_rings.asp

Cassini reveals new details about Saturn's rings
PPARC
September 5, 2005

Cassini scientists today (5th September 2005) announced a host of
fantastic new results from the spacecraft's first season of prime ring
viewing, including some unexpected findings on Saturn's rings. These
include new structures in Saturn's diffuse rings, clumps and knots in
the F ring - some of which may be small moons - and a completely
unexpected spiral ring around the planet in the vicinity of the F ring.

The findings are illustrated in processed images and movies being
released today and found at http://ciclops.org,
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

First in the line of new discoveries is that parts of the D ring
(Saturn's innermost ring) have relocated and dimmed. Images show one of
the major discrete ring structures in the D ring has changed in
brightness and moved inward towards Saturn by as much as 200 kilometres
(124 miles). A change over the 25 years since the NASA Voyager
spacecraft flybys indicates very short evolutionary lifetimes in the D
ring and is of great interest to ring scientists who have been hoping
that Cassini would yield information about ring ages and lifetimes.

Dr. Matt Hedman, an imaging team associate at Cornell University,
Ithaca, N.Y. said, "I think our Cassini images of the D ring are
providing new information about the dynamics and lifetimes of ring
particles in a new regime, very close to the planet."

The delicate G ring encircles the planet at about 170,000 kilometres
(106,000 miles) from Saturn's centre. Cassini scientists have now found
a discontinuous bright ring segment, or 'arc', in this ring that bear at
least a fleeting similarity to those imaged around Neptune in 1989 by
NASA's Voyager 2 spacecraft. Scientists think that long-lived arcs may
be created or maintained by a nearby hidden moon. Another thought is
that they formed as a result of a meteoroid impact.

Saturn's tenuous D and G rings contain very little material, and the
tiny, icy particles are the size of dust or smoke.

In examining the intriguing, knotted F ring, imaging team scientists
have also discovered that the ghostly ringlets flanking the ring's core
are arranged into a spiral structure wound like a spring around the
planet. Other spiralling structures seen in the main rings of Saturn,
the density and bending waves, are initiated by the gravitational
influence of an orbiting moon.

Density and bending waves move across the rings because of the way that
relatively massive ring particles exert a gravitational influence on
each other and can all move together. In contrast, the spiral structure
contains very little mass and appears to originate from material somehow
episodically ejected from the core of the F ring and then sheared out
due to the different orbital speeds followed by the constituent particles.

"It is a big surprise to see a spiral arm in Saturn's rings," said Dr.
Sebastien Charnoz, imaging team associate at the University of Paris.
"It is very possible that the spiral is a consequence of moons crossing
the F ring and spreading particles around, and may be telling us that
the F ring might be a very unstable or even an ephemeral structure."

In the same region, scientists continue to spot small, clump-like
features that may be loosely-bound clumps of material or tiny moonlets.
Some of them have been sighted for the better part of a year. The
solid-or-not nature of these mysterious F ring objects may be determined
by repeated sightings: moons will persist, while clumps are expected to
dissipate with time.

"We have long suspected that small moons were hiding among the F ring's
strands and producing some of the structures that we see," said Imaging
Team Member Professor Carl Murray of Queen Mary, University of London.
"But now the problem is that we are detecting objects that may be either
solid moons controlling the ring, or just loose clumps of particles
within the ring, and it's hard to tell the difference. It is like trying
to distinguish sheep dogs from sheep in a very large flock."

A puzzling characteristic of at least two of the clumps/moons is that
they appear to cross the F ring periodically. One of them, an object
that was discovered last year (S/2004 S6), may be responsible for
forming the spiral.

"If the orbit that we have computed for S/2004 S6 is correct, then it
must periodically plow through the core of the F ring," said Dr. Joseph
Spitale, an imaging team associate at the Space Science Institute in
Boulder, Colo. "The details of that interaction are not understood, but
there probably are observable consequences, and maybe the F ring spiral
is one of them."

These ring results were acquired over the summer as Cassini was in a
prime ring-viewing period where the spacecraft's orbit was raised to
look down on the rings. The discoveries began almost immediately, with
the discovery in May of a tiny moonlet orbiting within the narrow Keeler
Gap in Saturn's outer A ring.

These and other results were presented in a press briefing at the 37th
Annual Meeting of the Division for Planetary Sciences meeting held this
week in Cambridge, England.

Contacts

Gill Ormrod <gill.ormrod_at_pparc.ac.uk> - PPARC Press Office
Tel: 01793 442012. Mobile: 0781 8013509

Professor Carl Murray <c.d.murray_at_qmul.ac.uk>, Cassini Imaging
Team member, Queen Mary, University of London
Tel: 020 7882 5456. Mobile: 07976 243883.

Jacqueline Mitton -DPS Press Office, Cambridge (DPS runs from 4th-9th
September)
Tel: 07770 386133

Preston Dyches <media_at_ciclops.org> - Media Relations Office
Cassini Imaging Central Laboratory for Operations (CICLOPS
<http://ciclops.org>)
Space Science Institute, Boulder, Colorado
Tel: 00 1 (720) 974-5859

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory (JPL), a division of the California Institute of Technology
in Pasadena, manages the Cassini-Huygens mission for NASA's Science
Mission Directorate, Washington. The Cassini orbiter and its two onboard
cameras were designed, developed and assembled at JPL. The imaging team
consists of scientists from the U.S., England, France, and Germany. The
imaging operations center and team leader (Dr. C. Porco) are based at
the Space Science Institute in Boulder, Colo.
Received on Tue 06 Sep 2005 04:32:45 PM PDT