During a non-targeted flyby by the Cassini spacecraft of Saturn's moon
Enceladus on Nov. 26, 2005, Cassini's visual and infrared mapping
spectrometer measured the spectrum of the plumes originating from the
south pole of the icy moon.
The instrument captured a very clear signature of small ice particles in
the plume data, at the 2.9 micron wavelength. This image of Enceladus,
taken with the visual and infrared mapping spectrometer, shows not only
the plume over the south pole, but also the dark side of the moon,
silhouetted against a foggy background of light from the E Ring.
The bottom graph shows the measurements of the spectrum, of this
background light. It shows a very similar signature of small ice particles
to that in the plumes, confirming earlier expectations that Enceladus is
indeed the source of the E ring.
Preliminary analyses suggest that the average size of the particles in the
plume is about 10 microns (or 1/100,000 of a meter). The particles in the
E ring are about three times smaller. The sunlit surface of Enceladus
itself, visible as a thin crescent at the bottom of the image, is also
composed of water ice, but with a much larger grain size than the plume.
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 http://saturn.jpl.nasa.gov.
The visual and infrared mapping spectrometer team homepage is at http://wwwvims.lpl.arizona.edu.
