Saturn's Moon Iapetus Shows a Bulging Waistline
Images returned by NASA's Cassini spacecraft cameras during
a New Year's Eve flyby of Saturn's moon Iapetus show startling surface features that are fueling
heated scientific discussions about their origin.
Images returned by NASA's Cassini spacecraft cameras during
a New Year's Eve flyby of Saturn's moon Iapetus (eye-APP-eh-
tuss) show startling surface features that are fueling
heated scientific discussions about their origin.One of these features is a long narrow ridge that lies
almost exactly on the equator of Iapetus, bisects its entire
dark hemisphere and reaches 20 kilometers high (12 miles).
It extends over 1,300 kilometers (808 miles) from side to
side, along its midsection.  No other moon in the solar
system has such a striking geological feature.  In places,
the ridge is comprised of mountains.  In height, they rival
Olympus Mons on Mars, approximately three times the height
of Mt. Everest, which is surprising for such a small body as
Iapetus.  Mars is nearly five times the size of Iapetus.Images from the flyby are available athttp://saturn.jpl.nasa.gov,http://www.nasa.gov/cassiniandhttp://ciclops.org.Iapetus is a two-toned moon. The leading hemisphere is as
dark as a freshly-tarred street, and the white, trailing
hemisphere resembles freshly-fallen snow.The flyby images, which revealed a region of Iapetus never
before seen, show feathery-looking black streaks at the
boundary between dark and bright hemispheres that indicate
dark material has fallen onto Iapetus.  Opinions differ as
to whether this dark material originated from within or
outside Iapetus. The images also show craters near this
boundary with bright walls facing towards the pole and dark
walls facing towards the equator.Cassini's next close encounter with Iapetus will occur in
September 2007.  The resolution of images from that flyby
should be 100 times better than the ones currently being
analyzed.  The hope is that the increased detail may shed
light on Iapetus' amazing features and the question of
whether it has been volcanically active in the past.With a diameter of about 1,400 kilometers (890 miles),
Iapetus is Saturn's third largest moon. It was discovered by
Jean-Dominique Cassini in 1672. It was Cassini, for whom the
Cassini-Huygens mission is named, who correctly deduced that
one side of Iapetus was dark, while the other was white.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 Science Mission
Directorate, Washington, D.C. The Cassini orbiter and its
two onboard cameras were designed, developed and assembled
at JPL. The European Space Agency built and manages the
development of the Huygens probe and is in charge of the
probe operations. The Italian Space Agency provided the high-
gain antenna, much of the radio system and elements of
several of Cassini's science instruments. The imaging team
is based at the Space Science Institute, Boulder, Colo.