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Cassini
Images Mammoth Cloud Engulfing Titan's North Pole
A
giant cloud half the size of the United States has been imaged on
Saturn's moon Titan by the Cassini spacecraft. The cloud may be
responsible for the material that fills the lakes discovered last
year by Cassini's radar instrument.
Includes
Caption
Cassini
imaged a huge cloud system covering the north pole of Titan.
Image
credit: NASA/JPL/University of Arizona
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Cloaked by winter's
shadow, this cloud has now come into view as winter turns to
spring. The cloud extends down to 60 degrees north latitude, is
roughly 2,400 kilometers (1,490 miles) in diameter and engulfs
almost the entire north pole of Titan.
The new image was
acquired on Dec. 29, 2006, by Cassini's visual and infrared
mapping spectrometer. Scientific models predicted this cloud
system, but it had never been imaged in such detail before.
"We
knew this cloud had to be there but were amazed at its size and
structure," said Dr. Christophe Sotin of the University of
Nantes, France, a member of the visual and infrared mapping
spectrometer team and distinguished visiting scientist at NASA's
Jet Propulsion Laboratory, Pasadena, Calif. "This cloud
system may be a key element in the global formation of organics
and their interaction with the surface."
The same
cloud system seen on Dec. 29, was still there two weeks later
during a Jan. 13, 2007, flyby, even though observing conditions
were slightly less favorable than in December.
The
Cassini radar team reported last year that the lakes at the north
pole are partly filled, and some appear to have evaporated,
likely contributing to this cloud formation, which is made up of
ethane, methane and other organics. These findings reinforce the
idea that methane rains down onto the surface to form lakes and
then evaporates to form clouds. Scientists compare this methane
cycle to the hydrological cycle on Earth, dubbing it
"methane-ologic cycle."
Ground-based
observations show this Titan cloud system comes and goes with the
seasons. A season on Titan lasts approximately seven Earth years.
Based on the global circulation models, it seems that such cloud
activity can last about 25 Earth years before almost vanishing
for four to five years, and then appearing again for 25 years.
Scientists expect this cloud to be around for several
years. As the seasons change, scientists expect a shift of these
clouds and lakes from the north pole to the south pole. On
Titan's south pole, scientists have seen only one kidney-shaped
lake with Cassini's imaging cameras.
"With 16 more
flybys to come this year, we should have the opportunity to
monitor the evolution of this cloud system over time," said
Dr. Stephane Le Mouelic, working with the Cassini visual and
infrared mapping spectrometer team, and also at the University of
Nantes.
The Cassini-Huygens mission is a cooperative
project of NASA, the European Space Agency and the Italian Space
Agency. JPL, 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,
Tucson.
Source
/ Credit: NASA
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