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Rosemary Sullivant/Carolina Martinez 818-354-5011
Jet Propulsion Laboratory, Pasadena, Calif.
NEWS RELEASE: 2008-001 Jan. 3, 2008
Hot Cyclones Churn at Both Ends of Saturn
Despite more than a decade of winter darkness, Saturn's north pole is home to an
unexpected hot spot remarkably similar to one at the planet's sunny south pole. The
source of its heat is a mystery. Now, the first detailed views of the gas giant's high
latitudes from the Cassini spacecraft reveal a matched set of hot cyclonic vortices, one at
each pole.
While scientists already knew about the hot spot at Saturn's south pole from previous
observations by the W. M. Keck Observatory in Hawaii, the north pole vortex was a
surprise. The researchers report their findings in the Jan. 4 issue of Science.
"We had speculated that the south pole hot spot was connected to the southern, sunlit
conditions," said Glenn Orton, a senior research scientist at NASA's Jet Propulsion
Laboratory, Pasadena, Calif., and co-investigator on Cassini's composite infrared
spectrometer. "Since the north pole has been deprived of sunlight since the arrival of
winter in 1995, we didn't expect to find a similar feature there."
The infrared data show that the shadowed north pole vortex shares much the same
structure and temperature as the one at the sunny south pole. The cores of both show a
depletion of phospine gas, an imbalance probably caused by air moving downward into
the lowest part of Saturn's atmosphere, the troposphere. Both polar vortices appear to be
long-lasting and intrinsic parts of Saturn and are not related to the amount of sunlight
received by one pole or the other.
"The hot spots are the result of air moving polewards, being compressed and heated up as
it descends over the poles into the depths of Saturn," said Leigh Fletcher, a planetary
scientist from the University of Oxford, England, and the lead author of the Science
paper. "The driving forces behind the motion, and indeed the global motion of Saturn's
atmosphere, still need to be understood."
Though similar, the two polar regions differ in one striking way. At the north pole, the
newly discovered vortex is framed by the distinctive, long-lived and still unexplained
polar hexagon. This mysterious feature encompassing the entire north pole was first
spotted in the 1980s by NASA's Voyager 1 and 2 spacecraft. Cassini's infrared cameras
also detected the hexagon in deep atmospheric clouds early in 2007.
In their paper, Fletcher and his colleagues report that the bright, warm hexagon is much
higher than previous studies had shown. "It extends right to the top of the troposphere,"
says Fletcher. "It is associated with downward motion in the troposphere, though the
cause of the hexagonal structure requires further study."
Winter lasts about 15 years on Saturn. Researchers anticipate that when the seasons
change in the coming years and Saturn's north pole is once again in sunlight, they will be
able to see a swirling vortex with high eye walls and dark central clouds like the one now
visible at the south pole. "But Saturn may surprise us again," says Fletcher.
"The fact that Neptune shows a similar south polar hot spot whets our appetite for the
strange dynamics of the poles of the other gas giants," Fletcher says.
More information about Jupiter's poles will come from NASA's Juno mission, currently
scheduled for launch in 2011 and arrival in 2016.
Fletcher's research was funded by the United Kingdom's Science and Technology
Facilities Council.
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 science team for Cassini's composite infrared spectrometer team is
based at NASA's Goddard Space Flight Center, Greenbelt, Md.
-end-
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