Encircled in purple stratospheric haze, Titan appears as a softly glowing
sphere in this colorized image taken one day after Cassini’s first flyby of
the moon on July 2, 2004.
This image shows a thin, detached haze layer that appears to float
above the main atmospheric haze. Because of its thinness, the high
haze layer is best seen at the moon’s limb. NASA's Voyager spacecraft
detected such detached haze layers on Titan during their flybys in the
early 1980s.
The image, which shows Titan’s southern polar region, was taken
using a spectral filter sensitive to wavelengths of ultraviolet light
centered at 338 nanometers. The image has been false-colored
to approximate what the human eye might see were our vision
able to extend into the ultraviolet: The globe of Titan retains the
pale orange hue our eyes usually see, and both the main atmospheric
haze and the thin detached layer have been given their natural
purple color. The haze layers have been brightened for visibility.
The best possible observations of the detached layer are made in
ultraviolet light because the small haze particles which populate this
part of Titan’s upper atmosphere scatter short wavelengths more
efficiently than longer visible or infrared wavelengths. This accounts
for the bluish-purple color.
Images like this one reveal some of the key steps in the formation
and evolution of Titan's haze. The process begins in the high
atmosphere (at altitudes higher than 600 kilometers or 370 miles),
where solar ultraviolet light breaks down methane and nitrogen
molecules. The products react to form more complex organic molecules
containing carbon, hydrogen and nitrogen, and these in turn combine
to form the very small particles seen as high hazes. The small particles
stick upon collision with one another, forming larger particles which fall
deeper into the atmosphere to maintain the lower main haze layer which
is thick enough to obscure the surface at visible wavelengths. The
altitude of the detached haze layer observed by Cassini (near 500
kilometers or 310 miles) is significantly higher than the detached haze
seen by Voyager (at 300 to 350 kilometers or 185 to 215 miles). The
upward shift in haze altitude from Voyager to Cassini suggests the
possibility of seasonality in haze production or atmospheric circulation strength.
The image was taken with the Cassini spacecraft narrow-angle camera on
July 3, 2004, at a distance of about 789,000 kilometers (491,000 miles) from
Titan and at a Sun-Titan-spacecraft, or phase, angle of 114 degrees. The
image scale is 4.7 kilometers (2.9 miles) per pixel.
[This caption was modified on March 16, 2005.]
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 imaging team is based at the Space Science Institute,
Boulder, Colo.
For more information about the Cassini-Huygens mission, visit
http://saturn.jpl.nasa.gov and the Cassini imaging team home page,
http://ciclops.org.
