Bright, wispy markings stretch across a region of darker terrain on
Saturn's moon Rhea. In this extreme false-color view, the roughly
north-south fractures occur within strips of material (which appear
greenish here) that are a different color from the surrounding cratered
landscape.
To create the false-color view, ultraviolet, green and infrared images
were combined into a single black and white picture that isolates and maps
regional color differences. Most of the large-scale variations in
brightness across the surface are removed by this process. This "color
map" was then superimposed over a clear-filter image.
The origin of the color differences is not yet understood, but it may be
caused by subtle differences in the surface composition or grain sizes
making up the icy soil.
Wispy markings were seen on the trailing hemispheres of both Rhea and
Dione in images taken by NASA's Voyager spacecraft, and were hypothesized
by some researchers to be the result of material extruded onto the surface
by ice volcanism. Cassini's earlier revelation of the braided fractures on
Dione led to speculation that Rhea's wisps might also be created by
fractures.
This view shows terrain on the trailing hemisphere of Rhea (1,528
kilometers, or 949 miles across). North is up.
The image was taken using the Cassini spacecraft narrow-angle camera on
Jan. 17, 2006, at a distance of approximately 245,000 kilometers (152,000
miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 30
degrees. Image scale is 1 kilometer (4,771 feet) per pixel.
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 operations center is based at the Space
Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/home/index.cfm. The Cassini imaging team
homepage is at http://ciclops.org.
