by Playfuls Staff |
28th March 2007
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. [more]
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 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.
Image Credit: NASA/JPL/University
of Arizona
