New images provided by the visual infrared mapping spectrometer on the
Cassini spacecraft reveal a diverse array of clouds in the depths of
Saturn.
This new view on the right side shows clouds at an altitude where pressure
is nearly 2 bar. A bar is a unit of atmospheric pressure equivalent to
Earth's sea-level atmospheric pressure. These clouds are about 30
kilometers (19 miles) underneath the clouds usually observed on Saturn.
This is distinctly different from the typical view of Saturn in reflected
sunlight, shown on the left. The left view is characterized by broad
expanses of clouds near the 1-bar level, such as the white cloud seen
circling the equator, with little hint of the discrete cloud complexes
lying underneath.
This new view was obtained at the 5-micron wavelength, using Saturn's own
thermal radiation emanating from Saturn's interior as the light source
instead of the Sun. Clouds at the 2-bar depth block this upwelling
radiation to varying degrees, depending on the thickness of the cloud. At
the 5-micron wavelength, the instrument sees such clouds as relatively
dark areas in its view of Saturn. To render them visible as white clouds
in the image shown on the right, the original view was photographically
inverted. This technique enables clouds to be imaged across the globe,
under both daytime and nighttime conditions. The images are also
unaffected by shadowing from Saturn's immense ring system, unlike the
left-hand image which has much of the northern hemisphere covered by ring
shadow.
These images were acquired by Cassini's visual infrared mapping
spectrometer on June 28, 2005, at a distance of 1.2 million kilometers
(745,645 miles), and at a solar phase angle of 102 degrees. The color
composite on the left comprises three images taken at different
wavelengths: 2.79 micron (red), 1.60 micron (green), and 2.05 micron
(blue). The image on the right was taken at 5.1 micron wavelength, with
the brightness inverted to reveal clouds as white and atmospheric
clearings as dark.
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 visual
and infrared mapping spectrometer team is based at the University of
Arizona.
For more information about the Cassini-Huygens mission http://saturn.jpl.nasa.gov.
The visual and infrared mapping spectrometer team homepage is at
http://wwwvims.lpl.arizona.edu.