These spectacular Cassini images of Saturn's moon Iapetus show an enticing
world of contrasts.
These are the sharpest views of Iapetus from Cassini so far, and they
represent better resolution than the best images of this moon achieved by
NASA's Voyager spacecraft. Images obtained using ultraviolet (centered at
338 nanometers), green (568 nanometers) and infrared (930 nanometers)
filters were combined to produce the enhanced color views at left and
center; the image at the right was obtained in visible white light. The
images on the bottom row are identical to those on top, with the addition
of an overlying coordinate grid.
These views show parts of the moon's anti-Saturn side--the side that
faces away from the ringed planet--which will not be imaged again by
Cassini until Sept., 2007. In the central view, part of the moon's
eastern edge was not imaged and appears to be cut off.
With a diameter of 1,436 kilometers (892 miles), Iapetus is Saturn's
third largest moon. It is famous for the dramatic contrasts in brightness
on its surface--the leading hemisphere is as dark as a freshly-tarred
street, and the trailing hemisphere and poles almost as bright as snow.
Many impact craters can be seen in the bright terrain and in the
transition zone between bright and dark, and for the first time in parts
of the dark terrain. Also visible is a line of mountains that appear as a
string of bright dots in the two color images at left, and on the eastern
limb in the image at right. These mountains were originally detected in
Voyager images, and might compete in height with the tallest mountains on
Earth, Jupiter's moon Io and possibly even Mars. Further observations
will be required to precisely determine their heights. Interestingly, the
line of peaks is aligned remarkably close to the equator of Iapetus.
The large circular feature rotating into view in the southern hemisphere
is probably an impact structure with a diameter of more than 400
kilometers (250 miles), and was first seen in low-resolution Cassini
images just two months earlier.
Theses images were taken with the Cassini spacecraft narrow angle camera
between Oct, 15 and 20, 2004, at distances of 1.2, 1.1 and 1.3 million
kilometers (746,000, 684,000 and 808,000 miles) from Iapetus,
respectively. The Sun-Iapetus-spacecraft, or phase, angle changes from
88 to 144 degrees across the three images. The image scale is
approximately 7 kilometers (4.5 miles) per pixel.
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 Cassini-Huygens mission for NASA's Office of Space
Science, 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.
