Figure 1
This image of the infrared heat radiation from Saturn's moon Iapetus was
obtained by the Cassini composite infrared spectrometer instrument 16
hours before Cassini's closest approach to this mysterious moon, on
December 31, 2004. The thermal radiation is shown as both a grayscale
image, equivalent to what we would see if our eyes were sensitive to
infrared wavelengths near 15 microns, and as a color-coded temperature
map. A previously-released mosaic obtained by Cassini's imaging camera
shortly before the composite infrared spectrometer observation, with
similar scale and orientation, is also shown for comparison.
Temperatures reach nearly 130 Kelvin (-226 Fahrenheit) at noon on the
equator on the dark material that covers most of this side of Iapetus,
making high noon on Iapetus's dark side probably the warmest places in
the Saturn system. This is much warmer than temperatures on another
Saturnian moon, Phoebe, measured by composite infrared spectrometer in
June 2004. Those Phoebe temperature measurements peaked near 112 Kelvin
(-258 Fahrenheit), because though Phoebe is almost as dark as Iapetus's
dark material and absorbs nearly as much sunlight, Phoebe rotates much
more quickly (once every 9 hours, compared to 79 days for Iapetus). That
means the surface has less time to heat up during the day. Temperatures
on Iapetus's bright material are much colder, peaking near 100 Kelvin
(-280 Fahrenheit), both because the bright material absorbs less sunlight
and because it is further from the equator on this side of Iapetus.
Temperatures in the large crater near the center of the disc are slightly
different from those in surrounding areas, because sloping surfaces
within the crater are warmer where they are tilted towards the Sun and
cooler when tilted away from the Sun.
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 and its two onboard cameras were
designed, developed and assembled at JPL. The composite infrared
spectrometer team is based at NASA's Goddard Space Flight Center,
Greenbelt, Md.
For more information about the Cassini-Huygens mission visit,
http://saturn.jpl.nasa.gov and the instrument team's home page,
http://cirs.gsfc.nasa.gov/..
