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Cassini Images Bizarre Hexagon
on Saturn
04/09/2007
From http://saturn.jpl.nasa.gov
Press
Release
(Additional comments below)
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.
For original article click
here
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See also the
forthcoming TPOD discussing the hexagon in relation to
plasma discharge configurations. |
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