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