During the July 14, 2005, flyby of Saturn's moon Enceladus, Cassini's
ultraviolet imaging spectrograph made the first direct detection of an
atmosphere, first suggested by Cassini magnetometer measurements.
The ultraviolet imaging spectrograph observed the star Gamma Orionis as
Enceladus crossed in front of the star. The light of the star dimmed as
it was obscured by the atmosphere before being blocked entirely by
Enceladus itself. The spectrum of the starlight changed as it passed
through the atmosphere, indicating the presence of water vapor.
The ultraviolet imaging spectrograph results suggest that the atmosphere
of Enceladus is not constant and may be consistent with a greater amount
of atmospheric gas near the south polar region. The presence of water
vapor is more consistent with warm water ice than with magnetospheric
sputtering.
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
ultraviolet imaging spectrograph was built at, and the team is based at
the University of Colorado, Boulder.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov. The ultraviolet imaging spectrograph team home
page is at http://lasp.colorado.edu/cassini.
