Click on image for larger annotated version
Cassini made a close flyby of Saturn's moon Iapetus on Sept. 10, 2007, and
the visual and infrared mapping spectrometer obtained these images during
that event.
These two images show a higher resolution version of the equatorial
region shown in PIA10010. The equatorial region includes the equatorial bulge
which shows no differences in these compositions compared to surrounding
regions.
The color image on the right shows the results of mapping for three
components of Iapetus' surface: carbon dioxide that is trapped or adsorbed
in the surface (red), water in the form of ice (green), and a
newly-discovered effect due to trace amount of dark particles in the ice
creating what scientists call Rayleigh scattering (blue). The Rayleigh
scattering effect is the main reason why the Earth's sky appears blue.
There is a complex transition zone from the dark region, on the right,
which is high in carbon dioxide, to the more ice-rich region on the left.
Some crater floors are filled with carbon dioxide-rich dark material. As
the ice becomes cleaner to the left, the small dark particles become more
scattered and increase the Rayleigh scattering effect, again indicative of
less than 2 percent dark sub-0.5-micron particles.
The visual and infrared mapping spectrometer is like a digital camera, but
instead of using three colors, it makes images in 352 colors, or
wavelengths, from the ultraviolet to the near-infrared. The many
wavelengths produce a continuous spectrum in each pixel, and these spectra
measure how light is absorbed by different materials. By analyzing the
absorptions expressed in each pixel, a map of the composition at each
location on the moon can be constructed.
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 was designed, developed and assembled at JPL. The Visual
and Infrared Mapping Spectrometer team is based at the University of
Arizona.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/home/index.cfm. The visual and infrared mapping
spectrometer team homepage is at http://wwwvims.lpl.arizona.edu.
