Saturn's Mysterious Hexagon Emerges from Winter Darkness
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Saturn's Mysterious Hexagon Emerges from Winter Darkness
Jet Propulsion Laboratory
December 09, 2009
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.
Jia-Rui C. Cook, 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui...@jpl.nasa.gov
Joe Mason, 720-974-5859
Space Science Institute, Boulder, Colo.
jma...@ciclops.org
2009-187