Original picture and caption are available at http://photojournal.jpl.nasa.gov/catalog/PIA05410 .

The Cassini spacecraft has taken the most detailed temperature
measurements to date of Saturn’s rings. Data taken by the
composite infrared spectrometer instrument on the spacecraft while
entering Saturn’s orbit show the cool and relatively warm regions of
the rings.

This false-color image shows that the temperatures on the unlit side
of Saturn’s rings vary from a relatively warm 110 Kelvin (-261 degrees
Fahrenheit, shown in red), to a cool 70 Kelvin (-333 degrees
Fahrenheit, shown in blue). The green represents a temperature
of 90 Kelvin (-298 degrees Fahrenheit). Water freezes at 273 Kelvin
(32 degrees Fahrenheit).

The data show that the opaque region of the rings, like the outer A
ring (on the far right) and the middle B ring, are cooler, while more
transparent sections, like the Cassini Division (in red just inside
the A ring) or the inner C ring (shown in yellow and red), are
warmer. Scientists had predicted this might be the case, because
the opaque ring areas would let less light through, and the
transparent areas, more. These results also show, for the first
time, that individual ringlets in the C ring and the Cassini Division
are cooler than the surrounding, more transparent regions.

The temperature data were taken on July 1, 2004, shortly after Saturn
orbit insertion. Cassini is so close to the planet that no
pictures of the unlit side of the rings are available, hence the
temperature data was mapped onto a picture of the lit side of the
rings. Saturn is overexposed and pure white in this picture.
Saturn’s moon Enceladus is visible below the rings, toward the center.

The composite infrared spectrometer, one of 12 instruments on Cassini,
will measure infrared emissions from atmospheres, rings and
surfaces. This spectrometer will create vertical profiles of
temperature and gas composition for the atmospheres of Titan and
Saturn. During Cassini’s four-year tour, the instrument will
also gather information on the thermal properties and composition of
Saturn’s rings and icy moons.

Cassini-Huygens 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 and Mission
Directorate, Washington. The Cassini orbiter was designed, developed
and assembled at JPL. The Composite Infrared Spectrometer team is
based at NASA’s Goddard Space Flight Center, Greenbelt, Md.