Specially designed Cassini orbits place Earth and Cassini on opposite
sides of Saturn's rings, a geometry known as occultation. Cassini
conducted the first radio occultation observation of Saturn's rings on
May 3, 2005.
Three simultaneous radio signals of 0.94, 3.6, and 13 centimeter
wavelengths (Ka-, X-, and S-bands) were sent from Cassini through the
rings to Earth. The observed change of each signal as Cassini moved
behind the rings provided a profile of the distribution of ring material
and an optical depth profile.
This simulated image was constructed from the measured optical depth
profiles of the Cassini Division and ring A. It depicts the observed
structure at about 10 kilometers (6 miles) in resolution. Many radial
features evident across ring A, but especially exterior to the Encke and
Keeler gaps (the broad and narrow black bands on the right side of the
image), are wavy features called 'density waves.' They are caused by
gravitational interaction with moons outside ring A.
Color is used to represent information about ring particle sizes based on
the measured effects of the three radio signals. Shades of purple
indicate regions where there is a lack of particles less than 5
centimeters (about 2 inches) in diameter. Green and blue shades indicate
regions where there are particles of sizes smaller than 5 centimeters (2
inches) and 1 centimeter (less than one third of an inch), respectively.
Note the gradual increase in shades of green towards the outer edge of
ring A. It indicates gradual increase in the abundance of 5-centimeter
(2-inch) and smaller particles. Frequent collisions between large ring
particles in this dynamically active region likely fragment the larger
particles into more numerous smaller ones.
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 radio
science team is based at JPL.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov. For more information on the radio science team visit
http://saturn.jpl.nasa.gov/spacecraft/instruments-cassini-rss.cfm.
