Cassini Finds Prometheus a Sculptor of Saturn's Rings

Contact: Preston Dyches

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Space Science Institute

Cassini finds Prometheus a sculptor of Saturn's rings
October 26, 2005

New findings from members of the Cassini imaging team show that certain
prominent features in Saturn's narrow and contorted F ring can be
understood in terms of a simple gravitational interaction with the
small
moon Prometheus. The results are published in today's issue of the
journal "Nature."

The F ring is notorious for exhibiting unusual structures, like
"knots,"
"kinks," and "clumps" that continue to puzzle astronomers. Cassini
images have shown that the gravitational effect of Prometheus appears
to
produce regular patterns in the ring, including a series of channels or
gores in the tenuous ring material interior to the F ring core, and
"streamers" of particles that temporarily link the ring to the moon.

Prometheus is only about 100 kilometers (60 miles) wide and orbits just
interior to the F ring. The Cassini imaging scientists' findings show
that Prometheus causes the structure as the moon approaches and recedes
from the F ring every 14.7 hours, during its orbit of Saturn.

As an example of a satellite that enters a ring on a regular basis, the
phenomenon posed unique challenges to the understanding of
ring-satellite interactions.

Using Cassini data, the team developed a model that shows the mechanism
by which Prometheus, as it recedes from its closest approach to the F
ring, gravitationally extracts material from the ring. The affected
particles do not escape the F ring region; rather, the changes to their
orbits produced by Prometheus cause them to oscillate back and forth
across the ring. One orbital period after the encounter, the effect is
visible as a dark channel or "gore" in the interior of the F ring, and
drape-like structures between the channels - in excellent agreement
with
Cassini images. In this way, Prometheus leaves its mark on the F ring
long after the satellite has moved on.

Dr. Carl Murray from Queen Mary, University of London, lead author of
the paper and member of the Cassini Imaging Science Subsystem team
said,
"As the closer and more massive of the F ring's two shepherding
satellites, Prometheus was always the likely culprit for causing
changes
to this narrow ring. Our model provides a plausible mechanism for the
origin of intricate structures detected in the F ring and suggests that
streamers, channels and a variety of other phenomena can all be
understood in terms of the simple gravitational effect of a satellite
on
ring particles."

Over time Prometheus is expected to dive deeper into the F ring - with
more extreme perturbations - culminating in December 2009 when the two
orbits approach their minimum separation.

Dr. Joseph Burns, an imaging team member from Cornell University,
Ithaca, N.Y. and also one of the paper's co-authors said, "We're eager
to learn what the satellite will do to this narrow, already contorted
ring, and in turn whether the ring particles will strike Prometheus,
changing its surface."

Murray added, "We see the model we have developed very much as a first
step in understanding the processes at work. Ultimately this type of
research will help us to understand how planets form and evolve."

The work described in the Nature paper is a collaboration between
Cassini imaging scientists at Queen Mary, University of London, Cornell
University and the Space Science Institute.

A new image of the F ring is 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 (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.