Spring Reveals Saturn's Hexagon Jet Stream
December 9, 2009, Source:
NASA Cassini-Huygens Mission to Saturn
This movie from Cassini, made possible only as
Saturn's north pole emerged from winter darkness, shows
new details of a jet stream that follows a
hexagon-shaped path and has long puzzled scientists.
The hexagon was hidden in darkness during the winter of
Saturn's long year, a year that is equal to about 29
Earth years. But as the planet approached its August
2009 equinox and signaled the start of northern spring,
the hexagon was revealed to Cassini's cameras. This is
the first time the whole hexagonal shape has been mapped
out in visible light by Cassini, and these images show
unprecedented details of Saturn's high northern
latitudes. The hexagon was originally discovered in
images taken by Voyager spacecraft in the early 1980s.
Since 2006, the Cassini Visual and Infrared Mapping
Spectrometer (VIMS) instrument has been observing the
hexagon at infrared wavelengths, but at lower spatial
resolution than these visible light images.
Three large mosaics were used to create this three-frame
movie. The mosaics used dozens of images and the
constituent images were projected into polar projections
to provide a complete view of the hexagon. The mosaics
used in this movie do not show the region directly
around the north pole because it had not yet fully
emerged from the polar winter night. Seams between the
images are visible in the third frame of the movie
because the observation geometry in those images made
removal of the seams difficult.
The six-sided shape remains a mystery. Scientists think
the hexagon is a meandering jet stream at 77 degrees
north latitude, but they don't know what controls the
path the stream takes. These images also show new
phenomena for scientists to decipher, such as waves that
can now be seen radiating from the corners of the
hexagon where the jet takes its hardest turns. These
images confirm the presence of a multi-walled structure
in each of the hexagon's six sides, and the structure
now can be seen extending to the top of Saturn's cloud
layer. The images show that the inside of the hexagon is
darker than the outside. The new images also show a
large spot inside the hexagon that could be related to a
dark spot seen inside the hexagon in 2006 in an image
taken by Cassini's VIMS instrument. An earlier Voyager
mosaic showed a large spot outside the hexagon. That
spot existed at least until 1991 before disappearing
into the long winter polar night.
Images from Voyager and from ground-based telescopes
suffered from poor viewing perspectives. In late 2006,
Cassini's VIMS camera imaged the region in the thermal
infrared wavelength, showing the hexagon in false color.
Multiple images acquired by the VIMS instrument over a
12-day period showed that the feature is nearly
stationary and is likely an unusually strong
pole-encircling planetary wave that extends deep into
the atmosphere. Scientists had speculated that a large
vortex seen outside the hexagon during the Voyager
observations exerted forces on the jet stream making it
adopt a hexagonal pattern in a manner similar to how jet
streams on Earth divert around high-pressure systems.
However, in these new images, the vortex is notably
absent while the hexagon persists almost 30 years after
it was first seen.
The images were taken in visible light with the Cassini
spacecraft wide-angle camera on Jan. 3, 2009. The images
were obtained at a distance of approximately 764,000
kilometers (475,000 miles) from Saturn. The smallest
resolved features at the latitude of the hexagon have a
horizontal scale of approximately 100 kilometers.
The Cassini-Huygens mission is a cooperative project of
NASA, the European Space Agency and the Italian Space
Agency. JPL manages the mission for the Science Mission
Directorate at NASA Headquarters in 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.
For more information about the Cassini-Huygens mission
visit http://saturn.jpl.nasa.gov.
The Cassini imaging team homepage is at http://ciclops.org.
Image credit: NASA/JPL/Space Science Institute
Saturn�s Hexagon May Be Solar System�s Coolest Mystery
December 9, 2009, Source:
Waired.com by Alexis Madrigal.
The Cassini spacecraft has returned the best images yet of the strange hexagonal jet stream that flows around the northern pole of Saturn.
First discovered by the Voyager spacecraft in the early 1980s, the hexagon remains a beautiful mystery to astronomers, and one they�ve been waiting for another shot to see for almost three decades.
�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 project researcher at the California Institute of Technology, in a NASA release. �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 circles Saturn at 77 degrees north and is wider than two Earths. Nearly everything about the weather pattern is baffling. First, it�s unclear what causes the hexagon. Second, it�s bizarre that the jet stream would make such sharp turns. Earth�s atmospheric movements rarely display such geometric rigor.
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