Cassini captures the first high-resolution glimpse of the bright trailing
hemisphere of Saturn's moon Iapetus.
This false-color mosaic shows the entire hemisphere of Iapetus (1,468
kilometers, or 912 miles across) visible from Cassini on the outbound leg
of its encounter with the two-toned moon in Sept. 2007. The central
longitude of the trailing hemisphere is 24 degrees to the left of the
mosaic's center.
Also shown here is the complicated transition region between the dark
leading and bright trailing hemispheres. This region, visible along the
right side of the image, was observed in many of the images acquired by
Cassini near closest approach during the encounter.
Revealed here for the first time in detail are the geologic structures
that mark the trailing hemisphere. The region appears heavily cratered,
particularly in the north and south polar regions. Near the top of the
mosaic, numerous impact features visible in NASA Voyager 2 spacecraft
images (acquired in 1981) are visible, including the craters Ogier and
Charlemagne.
The most prominent topographic feature in this view, in the bottom half of
the mosaic, is a 450-kilometer (280-mile) wide impact basin, one of at
least nine such large basins on Iapetus. In fact, the basin overlaps an
older, similar-sized impact basin to its southeast.
In many places, the dark material--thought to be composed of
nitrogen-bearing organic compounds called cyanides, hydrated minerals and
other carbonaceous minerals--appears to coat equator-facing slopes and
crater floors. The distribution of this material and variations in the
color of the bright material across the trailing hemisphere will be
crucial clues to understanding the origin of Iapetus' peculiar bright-dark
dual personality.
The view was acquired with the Cassini spacecraft narrow-angle camera on
Sept. 10, 2007, at a distance of about 73,000 kilometers (45,000 miles)
from Iapetus.
The color seen in this view represents an expansion of the wavelengths of
the electromagnetic spectrum visible to human eyes. The intense
reddish-brown hue of the dark material is far less pronounced in true
color images. The use of enhanced color makes the reddish character of
the dark material more visible than it would be to the naked eye.
This mosaic consists of 60 images covering 15 footprints across the
surface of Iapetus. The view is an orthographic projection centered on
10.8 degrees south latitude, 246.5 degrees west longitude and has a
resolution of 426 meters (0.26 miles) per pixel. An orthographic view is
most like the view seen by a distant observer looking through a telescope.
At each footprint, a full resolution clear filter image was combined with
half-resolution images taken with infrared, green and ultraviolet spectral
filters (centered at 752, 568 and 338 nanometers, respectively) to create
this full-resolution false color mosaic.
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 operations center is based at the Space
Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/home/index.cfm. The Cassini imaging
team homepage is at http://ciclops.org.
