The magnetospheric imaging instrument onboard Cassini recently discovered
a new radiation belt just above Saturn's cloud tops, up to the inner edge
of the D-ring. Before this discovery, it was not anticipated that such a
trapped ion population could be sustained inside the rings.
This new radiation belt extends around the planet. It was detected by the
emission of fast neutral atoms created as its energetic ions interact with
gas clouds in the same region. Saturn's radiation belts have numerous
"holes" in them, created as the trapped ions collide with moons, dust
ring, and gas. With this discovery, the radiation belts are shown to
extend far closer to the planet than their previously known inner
boundary, which lies just at the outer edge of the main ring system. The
new belts are much smaller and much less energetic than the main radiation
belts. The main belts extend from about 139,000 kilometers (86,000 miles)
from Saturn's center out to about 362,000 (225,000 miles) and contain
particles with energies up to tens of mega-electron volts. The new belt
extends less than 6,000 kilometers (about 4,000 miles) in thickness, and
is not known to contain particles above about 150 kilo-electron Volts
total energy.
Shown here is an image taken by the magnetospheric imaging instrument on
July 1, 2004, from a distance of 24,000 kilometers (14,900 miles) from
Saturn's cloud tops. From blue to red the colors represent increasing
intensity of the radiation. The location of the moon Titan in the image
is shown, but emissions associated with Titan itself are too weak to
stand out in the intense emission from the main radiation belt. The
magenta lines represent the magnetic field lines that cross the equator
just at the inner edge of the D-Ring, where the new-found radiation belt
resides.
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 Science Mission
Directorate, Washington, D.C. The Cassini orbiter was designed, developed
and assembled at JPL. The magnetospheric imaging instrument was designed,
built and is operated by an international team lead by the Applied Physics
Laboratory of the Johns Hopkins University, Laurel, Md.
For more information about the Cassini-Huygens mission, visit
http://saturn.jpl.nasa.gov and the instrument team's home page,
http://sd-www.jhuapl.edu/CASSINI/index.html.