A collection of new ring phenomena, first observed in the sequence of
images taken of the dark side of Saturn's rings immediately after Cassini
entered orbit, may be evidence of the clumping and aggregation of ring
particles. This phenomena is caused by the combined gravitational effects
of Saturn, orbiting moons, and other ring particles.
Image A displays an unusual mottled-looking narrow region, with a radial
width varying with longitude from 5 to 10 kilometers (3 to 6 miles), seen
for the first time about 60 kilometers (37 miles) inside the outer edge of
Saturn's A ring. The resolution of this dayside image is about 1 kilometer
(0.6 miles) per pixel. Image B is a close-up of the region, mapped into a
longitude-radius system and contrast enhanced. The region is characterized
by blotchy light and dark areas about 30 to 40 kilometers (19 to 25 miles)
in longitudinal extent. The observed longitudinal extent of this region is
about 3.5 degrees.
The mottled regions also are probably caused by particle clumping brought
about by gravitational disturbances. The outer A ring edge is sculpted
into a seven-lobed pattern called a Lindblad resonance (a type of
dynamical resonance that occurs in rings systems) with the co-orbital
satellites Janus and Epimetheus. The resonant perturbations in this
region are complicated by the presence of these two moons whose orbits
are within 50 kilometers (31 miles) of each other.
Image C is a dark-side image of the outer edge of the Encke gap, with a
resolution of about 270 meters (886 feet) pixel, taken 18 degrees
upstream from the moon Pan, which inhabits the gap. The regularly spaced,
narrow dark lanes observed here are the wakes caused by Pan. Rope-like
features can be seen between the first two wakes nearest the gap edge.
These features are unique in all Cassini images taken so far. They
generally are between 10 and 20 kilometers (6 and 12 miles) long.
In their orbits around Saturn, the particles comprising the rings in this
region pass through the Pan wakes. When they do so, they are forced closer
together than usual. These ropy features appear to be a product of the
enhanced gravitational disturbances that occur when the particles pass
through the wakes caused by Pan and consequently are squeezed close
together. These disturbances obviously persist even outside the wakes, as
is evident here in the presence of the ropy structures in the bands in
between the wakes.
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,
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.
For more information about the Cassini-Huygens mission, visit
http://saturn.jpl.nasa.gov and the Cassini imaging team home page,
http://ciclops.org.