Images like this one, showing bright wispy streaks thought to be ice
revealed by subsidence of crater walls, are leading to the view that
Phoebe is an ice-rich body overlain with a thin layer of dark material.
Obvious down slope motion of material occurring along the walls of the
major craters in this image is the cause for the bright streaks, which
are over-exposed here. Significant slumping has occurred along the crater
wall at top left.
The slumping of material might have occurred by a small projectile
punching into the steep slope of the wall of a pre-existing larger
crater. Another possibility is that the material collapsed when triggered
by another impact elsewhere on Phoebe. Note that the bright, exposed
areas of ice are not very uniform along the wall. Small craters are
exposing bright material on the hummocky floor of
the larger crater.
Elsewhere on this image, there are local areas of outcropping along the
larger crater wall where denser, more resistant material is located.
Whether these outcrops are large blocks being exhumed by landslides or
actual 'bedrock' is not currently understood.
The crater on the left, with most of the bright streamers, is about 45
kilometers (28 miles) in diameter, front to back as viewed. The larger
depression in which the crater sits is on the order of 100 kilometers
(62 miles) across. The slopes from the rim down to the hummocky floor
are approximately 20 kilometers (12 miles) long; many of the bright
streamers on the crater wall are on the order of 10 kilometers (6 miles)
long. A future project for Cassini image scientists will be to work out
the chronology of slumping events in this scene.
This image was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 78
degrees, and from a distance of 11,918 kilometers (7,407 miles). The
image scale is approximately 70 meters (230 feet) per pixel. No
enhancement was performed on this image.
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 Office of Space
Science, 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.
