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Posted by on March 27, 2007, 2:10 pm
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http://www.jpl.nasa.gov/news/news.cfm?release=2007-034
Cassini Images Bizarre Hexagon on Saturn
Jet Propulsion Laboratory
March 27, 2007
Pasadena, Calif. -- An odd, six-sided, honeycomb-shaped feature
circling
the entire north pole of Saturn has captured the interest of
scientists
with NASA's Cassini mission.
NASA's Voyager 1 and 2 spacecraft imaged the feature over two decades
ago. The fact that it has appeared in Cassini images indicates that it
is a long-lived feature. A second hexagon, significantly darker than
the
brighter historical feature, is also visible in the Cassini pictures.
The spacecraft's visual and infrared mapping spectrometer is the first
instrument to capture the entire hexagon feature in one image.
"This is a very strange feature, lying in a precise geometric fashion
with six nearly equally straight sides," said Kevin Baines,
atmospheric
expert and member of Cassini's visual and infrared mapping
spectrometer
team at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We've
never
seen anything like this on any other planet. Indeed, Saturn's thick
atmosphere where circularly-shaped waves and convective cells dominate
is perhaps the last place you'd expect to see such a six-sided
geometric
figure, yet there it is."
The hexagon is similar to Earth's polar vortex, which has winds
blowing
in a circular pattern around the polar region. On Saturn, the vortex
has a hexagonal rather than circular shape. The hexagon is nearly
25,000
kilometers (15,000 miles) across. Nearly four Earths could fit inside
it.
The new images taken in thermal-infrared light show the hexagon
extends
much deeper down into the atmosphere than previously expected, some
100
kilometers (60 miles) below the cloud tops. A system of clouds lies
within the hexagon. The clouds appear to be whipping around the
hexagon
like cars on a racetrack.
"It's amazing to see such striking differences on opposite ends of
Saturn's poles," said Bob Brown, team leader of the Cassini visual and
infrared mapping spectrometer, University of Arizona, Tucson. "At the
south pole we have what appears to be a hurricane with a giant eye,
and
at the north pole of Saturn we have this geometric feature, which is
completely different."
The Saturn north pole hexagon has not been visible to Cassini's visual
cameras, because it's winter in that area, so the hexagon is under the
cover of the long polar night, which lasts about 15 years. The
infrared
mapping spectrometer can image Saturn in both daytime and nighttime
conditions and see deep inside. It imaged the feature with thermal
wavelengths near 5 microns (seven times the wavelength visible to the
human eye) during a 12-day period beginning on Oct. 30, 2006. As
winter
wanes over the next two years, the feature may become visible to the
visual cameras.
Based on the new images and more information on the depth of the
feature, scientists think it is not linked to Saturn's radio emissions
or to auroral activity, as once contemplated, even though Saturn's
northern aurora lies nearly overhead.
The hexagon appears to have remained fixed with Saturn's rotation rate
and axis since first glimpsed by Voyager 26 years ago. The actual
rotation rate of Saturn is still uncertain.
"Once we understand its dynamical nature, this long-lived, deep-seated
polar hexagon may give us a clue to the true rotation rate of the deep
atmosphere and perhaps the interior," added Baines.
The hexagon images and movie, including the north polar auroras are
available at: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov
and http://wwwvims.lpl.arizona.edu .
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. The Cassini orbiter was designed, developed
and
assembled at JPL. The Visual and Infrared Mapping Spectrometer team is
based at the University of Arizona.
------------------------------------------------------------------------
Media contact: Carolina Martinez/Jane Platt 818-354-9382/818-354-0880
Jet Propulsion Laboratory, Pasadena, Calif.
2007-034
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