Carolina Martinez (818)
354-9382
Jet Propulsion Laboratory, Pasadena,
Calif.
Laura K. Kraft (808)
885-7887
W. M. Keck Observatory,
Mauna Kea, Hawaii
Press
Release: 2005-020
February 3, 2005
Saturn's Bull's-Eye Marks its
Hot Spot
NASA astronomers using the
Keck I telescope in Hawaii are learning much more about a strange, thermal
"hot spot" on the tip of Saturn's south pole.
In the most precise reading
of Saturn's temperatures ever taken from Earth, a new set of infrared
images suggests a warm "polar vortex" at Saturn's south pole - the first
warm polar cap ever to be discovered in the solar system. The vortex is punctuated by a
compact spot that is the warmest place on the planet. The
researchers report their findings in the Feb. 4 issue of the journal
Science.
The images can be viewed
at: http://www.nasa.gov/multimedia/imagegallery/
.
A polar vortex is a
persistent, large-scale weather pattern, likened to a jet stream on Earth
in the upper atmosphere. On Earth, the Arctic Polar Vortex is typically
located over eastern Canada and plunges arctic air to the northern plains
in the United States. Earth's
cold Antarctic Polar Vortex, centered over Antarctica, traps air and
creates unusual chemistry, such as the effects that create the "ozone
hole".
Polar vortices on Earth,
Jupiter, Mars and Venus are colder than their surroundings. But new
images from the W. M. Keck Observatory show the first evidence of such a
polar vortex at much warmer temperatures than their
surroundings. And the even warmer, compact region at the pole
itself is quite unusual.
"There is nothing like this
compact warm 'cap' in the Earth's atmosphere," said Dr. Glenn S. Orton,
senior research scientist at NASA's Jet Propulsion Laboratory in Pasadena,
Calif., and lead author of the paper. "Meteorologists have detected sudden
warming of the pole, but on Earth this effect is very short-term.
This phenomenon on Saturn is longer-lived because we've been seeing hints
of it in our data for at least two years."
Data for these observations
were taken in the imaging mode of the Keck facility instrument, the Long
Wavelength Spectrometer, on Feb. 4, 2004, by Orton and Dr. Padma
Yanamandra-Fisher, the paper's co-author, also a research scientist at
JPL.
The puzzle isn't that
Saturn's south pole is warm; after all, it has been exposed to 15 years of
continuous sunlight, having just reached its summer Solstice late in
2002. But both the distinct boundary of a warm polar vortex some 30
degrees latitude from the southern pole and a very hot "tip" right at the
pole were completely unexpected. If the increased southern temperatures
are the result of the seasonal variations of sunlight, then temperatures
should increase gradually with increasing latitude. But they don't –
the tropospheric temperature increases toward the pole abruptly near 70
degrees latitude from 88 to 89 Kelvin (-301 to -299 degrees Fahrenheit)
and then to 91 Kelvin (-296 degrees Fahrenheit) right at the pole.
Near 70 degrees latitude, the stratospheric temperature increases even
more abruptly from 146 to 150 Kelvin (-197 to -189 degrees Fahrenheit) and
then again to 151 Kelvin (-188 degrees Fahrenheit) right at the pole.
The abrupt temperature
changes may be caused by a concentration of sunlight-absorbing
particulates trapping heat in Saturn's upper atmosphere. This theory
would explain why the hot spot appears dark in visible light and contains
the highest measured temperatures on Saturn. However, this alone
would not explain why the particles themselves are constrained to a
compact area at Saturn's south pole. One possible explanation would
be downwelling of dry air, which is also consistent with deeper clouds
observed at the southern pole. Researchers plan more observations
to check that possibility.
More detail about the
temperatures and possible chemical changes in these regions may be
available from an infrared spectrometer on the Cassini spacecraft, in
orbit around Saturn. The
discovery of the hot spot at Saturn's south pole has prompted Cassini's
composite infrared spectrometer science team, including Orton, to redirect
some future observations to this area.
"One of the obvious
questions is whether Saturn's north pole is abnormally cold and whether a
cold polar vortex has been established there. That's something we
can't see from Earth, and Cassini's instruments will be in a unique
position to observe it," said Orton.
Funding for this research
was provided by NASA's Office of Space Sciences and
Applications, Planetary
Astronomy Discipline, and the NASA Cassini project. The Cassini-Huygens mission is a
cooperative project of NASA, the European Space Agency and the Italian
Space Agency. The Jet Propulsion Laboratory, a division of the California
Institute of Technology in Pasadena, manages the Cassini-Huygens mission
for NASA's Science Mission Directorate, Washington, D.C.
The
W.M. Keck Observatory is operated by the California Association for
Research in Astronomy, a non-profit scientific partnership of the
California Institute of Technology, the University of California, and
NASA. On the Web at www.keckobservatory.org
.
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