Saturn's Mysterious Hexagon Emerges from Winter Darkness

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Jia-Rui C. Cook, 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook@jpl.nasa.gov

Joe Mason, 720-974-5859
Space Science Institute, Boulder, Colo.
jmason@ciclops.org

IMAGE/VIDEO ADVISORY:2009-187 December 9, 2009

Saturn's Mysterious Hexagon Emerges from Winter Darkness

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2009-187&cid=advisory_2009-187

After waiting years for the sun to illuminate Saturn's north pole again, cameras aboard
NASA's Cassini spacecraft have captured the most detailed images yet of the intriguing
hexagon shape crowning the planet.

The new images of the hexagon, whose shape is the path of a jet stream flowing around the
north pole, reveal concentric circles, curlicues, walls and streamers not seen in previous
images. Images and the three-frame animation are available at http://www.nasa.gov/cassini ,
http://saturn.jpl.nasa.gov and http://ciclops.org .

The last visible-light images of the entire hexagon were captured by NASA's Voyager
spacecraft nearly 30 years ago, the last time spring began on Saturn. After the sunlight faded,
darkness shrouded the north pole for 15 years. Much to the delight and bafflement of Cassini
scientists, the location and shape of the hexagon in the latest images match up with what they
saw in the Voyager pictures.

"The longevity of the hexagon makes this something special, given that weather on Earth
lasts on the order of weeks," said Kunio Sayanagi, a Cassini imaging team associate at the
California Institute of Technology. "It's a mystery on par with the strange weather conditions
that give rise to the long-lived Great Red Spot of Jupiter."

The hexagon was originally discovered in images taken by the Voyager spacecraft in the early
1980s. It encircles Saturn at about 77 degrees north latitude and has been estimated to have a
diameter wider than two Earths. The jet stream is believed to whip along the hexagon at
around 100 meters per second (220 miles per hour).

Early hexagon images from Voyager and ground-based telescopes suffered from poor
viewing perspectives. Cassini, which has been orbiting Saturn since 2004, has a better angle
for viewing the north pole. But the long darkness of Saturnian winter hid the hexagon from
Cassini's visible-light cameras for years. Infrared instruments, however, were able to obtain
images by using heat patterns. Those images showed the hexagon is nearly stationary and
extends deep into the atmosphere. They also discovered a hotspot and cyclone in the same
region.

The visible-light cameras of Cassini's imaging science subsystem, which have higher
resolution than the infrared instruments and the Voyager cameras, got their long-awaited
glimpse of the hexagon in January, as the planet approached equinox. Imaging team scientists
calibrated and stitched together 55 images to create a mosaic and three-frame movie. The
mosaics do not show the region directly around the north pole because it had not yet fully
emerged from winter night at that time.

Scientists are still trying to figure out what causes the hexagon, where it gets and expels its
energy and how it has stayed so organized for so long. They plan to search the new images
for clues, taking an especially close look at the newly identified waves that radiate from the
corners of the hexagon -- where the jet takes its hardest turns -- and the multi-walled
structure that extends to the top of Saturn's cloud layer in each of the hexagon's six sides.
Scientists are also particularly intrigued by a large dark spot that appeared in a different
position in a previous infrared image from Cassini. In the latest images, the spot appears in
the 2 o'clock position.

Because Saturn does not have land masses or oceans on its surface to complicate weather the
way Earth does, its conditions should give scientists a more elementary model to study the
physics of circulation patterns and atmosphere, said Kevin Baines, an atmospheric scientist at
NASA's Jet Propulsion Laboratory, Pasadena, Calif., who has studied the hexagon with
Cassini's visual and infrared mapping spectrometer.

"Now that we can see undulations and circular features instead of blobs in the hexagon, we
can start trying to solve some of the unanswered questions about one of the most bizarre
things we've ever seen in the solar system," Baines said. "Solving these unanswered
questions about the hexagon will help us answer basic questions about weather that we're still
asking about our own planet."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency
and the Italian Space Agency. JPL, a division of Caltech, manages the Cassini mission for
NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard
cameras were designed, developed and assembled at JPL. The imaging team is based at the
Space Science Institute, Boulder, Colo.

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