Cassini Finds Treasures Among the Rings and Small Satellites of Saturn

http://ciclops.lpl.arizona.edu/view.php?id=895

CASSINI FINDS TREASURES AMONG THE RINGS AND SMALL SATELLITES OF SATURN

MEDIA RELATIONS OFFICE
CASSINI IMAGING CENTRAL LABORATORY FOR OPERATIONS (CICLOPS)
SPACE SCIENCE INSTITUTE, BOULDER, COLORADO
http://ciclops.org


Preston Dyches (720) 974-5823
CICLOPS/Space Science Institute, Boulder, Colo.

For Immediate Release: February 24, 2005

CASSINI FINDS TREASURES AMONG THE RINGS AND SMALL SATELLITES OF SATURN

The high porosity of Saturn's innermost small moons, tenuous ringlets
discovered in some of the gaps in its rings, the variation in ring
particle composition across the rings, and new ring structures which
indicate more clearly than ever the transient clumping and aggregation
of particles as they orbit Saturn are among the discoveries being
reported today in the journal Science by the Cassini Imaging Science
team.

The Cassini imaging scientists have spent the last year analyzing
images
acquired by the Saturn orbiter's camera system beginning last February,
when routine imaging of Saturn and its rings and moons began. This
collection includes the most detailed images ever collected, taken
immediately after the Saturn orbit insertion maneuver, when the
spacecraft Cassini flew closer to the rings than any previous
spacecraft. This treasure trove of data has yielded surprising results
which will, with further study, improve scientists' understanding of
how
Saturn's rings actually work.

Ring features never before observed have been found in many of the
images. Weak, linear density waves excited in the rings by the small
moons, Atlas and Pan, have been examined and have yielded satellite
masses more reliable than previous measures. These new masses imply
that
Atlas and Pan are very porous - perhaps constructed like rubble-piles -
and similar in this regard to the other moons orbiting just outside
Saturn's rings, such as the moons that shepherd the F ring, Prometheus
and Pandora. These low densities suggest that all the close-in
satellites have been gravitationally pulled together out of smaller
bits
and pieces.

The examination of these same linear density waves, which lie in the
Cassini division in Saturn's rings, indicates that this rarefied region
of the rings, like Saturn's C ring, is populated with particles which
are on average smaller than particles in the A and B rings, two major
rings lying on either side of the Cassini division. The Cassini
division
material seems also to be vertically thinner - only several meters
(yards) - than the A or B rings. Other features, like "rope-like",
10-kilometer (6-mile) scale structures found in the outer edge of the
Encke gap, and splotchy, 30-kilometer (20-mile) scale structures seen
near the edge of the A ring, are the newly-found evidence of transient
particle clumping - a finding that is key to understanding in full the
behavior of particles under the influence of Saturn, orbiting moons and
other nearby particles.

Circumstantial evidence, in the form of spike-like features in the
outer
edge of the narrow Keeler gap in Saturn's A ring, is also presented
today that a tiny moon is likely to be found eventually orbiting dead
center in this gap. Imaging sequences have been planned to scour the
gaps in Saturn's rings for new moons. Imaging scientists expect that
eventually, they will find the moon hidden in the Keeler gap.

Several new faint rings have been sighted in Cassini images. One of
these, reported earlier, populates the same orbit as the small moon
Atlas; others lie in various gaps in the rings and may indicate the
presence of tiny embedded moons coincident with them or acting as
shepherds nearby. All of these saturnian diffuse rings are either
comparable to the jovian ring or more robust. Several of them are
spatially variable or kinked, likely evidence of the perturbations of
nearby moons.

Saturn's rings are primarily composed of water ice. But recently
analyzed multi-color images taken on approach to Saturn suggest more
strongly than ever that the amounts of rocky or organic contaminants in
the rings is often quite different in neighboring parts of the ring
system.

Finally, the new findings include refinements in the orbits of several
of Saturn's small satellites, some of them discovered by Cassini and
reported earlier. One especially intriguing result is the eccentric and
slightly inclined configuration of the orbit of the moon, Pan, which
maintains the Encke gap in Saturn's A ring. Until Cassini reached
Saturn, it wasn't clear if this moon's orbit would be circular or
eccentric. The shape is significant as it indicates the type of
interaction the moon has with the ring material surrounding it. If
Pan's
orbit can be kept eccentric by this interaction, then planets growing
in
a disk of material surrounding a star may also have eccentric orbits -
a
conclusion that may help explain the eccentric orbits of planets being
discovered today orbiting other stars in our galaxy.

Another reported finding is the observation that the tiny, 5 kilometer
(3 mile) -wide moon of Saturn, S/2004 S5 (recently named Polydeuces),
discovered by the imaging team and reported late last year, is in fact
a
Trojan moon of Dione. Saturn is the only planet known to have moons
with
smaller companion 'Trojan' moons. Trojan moons are those found near
stable 'Lagrange points', situated 60 degrees ahead or behind a larger
moon in its orbit around a planet. Helene is a previously-known
32-kilometer (20-mile) sized Trojan which orbits ahead of Dione,
usually
within 15 degrees of the leading Lagrange point; newly-discovered
Polydeuces can stray by as much as 32 degrees from Dione's trailing
Lagrange point. Dione is not alone in possessing Trojan moons - Tethys,
another of Saturn's moons also has a Trojan near each of its stable
Lagrange points. However, the wandering exhibited by Polydeuces is the
largest so far detected of any Trojan moon.

Images associated with this release, and information about the
Cassini-Huygens mission, are available at http://ciclops.org,
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

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, Washington, D.C. The Cassini orbiter and its two onboard
cameras were designed, developed and assembled at JPL. The imaging team
is based at the Space Science Institute, Boulder, Colo.