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NASA’s
Cassini spacecraft and a European Southern Observatory ground-based
telescope tracked the growth of a giant early-spring storm in Saturn’s
northern hemisphere that is so powerful it stretches around the entire
planet. The rare storm has been wreaking havoc for months and shooting
plumes of gas high into the planet’s atmosphere.
Cassini’s
radio and plasma wave science instrument first detected the large
disturbance, and amateur astronomers tracked its emergence in December
2010. As it rapidly expanded, its core developed into a giant, powerful
thunderstorm. The storm produced a 3,000-mile-wide
(5,000-kilometer-wide) dark vortex, possibly similar to Jupiter’s Great
Red Spot, within the turbulent atmosphere.
The
dramatic effects of the deep plumes disturbed areas high up in Saturn’s
usually stable stratosphere, generating regions of warm air that shone
like bright “beacons” in the infrared. Details are published in this
week’s edition of Science Magazine.
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“Nothing
on Earth comes close to this powerful storm,” says Leigh Fletcher, the
study’s lead author and a Cassini team scientist at the University of
Oxford in the United Kingdom. “A storm like this is rare. This is only
the sixth one to be recorded since 1876, and the last was way back in
1990.”
This
is the first major storm on Saturn observed by an orbiting spacecraft
and studied at thermal infrared wavelengths, where Saturn’s heat energy
reveals atmospheric temperatures, winds and composition within the
disturbance.
Temperature
data were provided by the Very Large Telescope (VLT) on Cerro Paranal
in Chile and Cassini’s composite infrared spectrometer (CIRS), operated
by NASA’s Goddard Space Flight Center in Greenbelt, Md.
“Our
new observations show that the storm had a major effect on the
atmosphere, transporting energy and material over great distances,
modifying the atmospheric winds — creating meandering jet streams and
forming giant vortices — and disrupting Saturn’s slow seasonal
evolution,” said Glenn Orton, a paper co-author, based at NASA’s Jet
Propulsion Laboratory in Pasadena, Calif.
The
violence of the storm — the strongest disturbances ever detected in
Saturn’s stratosphere — took researchers by surprise. What started as
an ordinary disturbance deep in Saturn’s atmosphere punched through the
planet’s serene cloud cover to roil the high layer known as the
stratosphere.
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“On
Earth, the lower stratosphere is where commercial airplanes generally
fly to avoid storms which can cause turbulence,” says Brigette Hesman, a
scientist at the University of Maryland in College Park who works on
the CIRS team at Goddard and is the second author on the paper. “If you
were flying in an airplane on Saturn, this storm would reach so high up,
it would probably be impossible to avoid it.”
Other
indications of the storm’s strength are the changes in the composition
of the atmosphere brought on by the mixing of air from different layers.
CIRS found evidence of such changes by looking at the amounts of
acetylene and phosphine, both considered to be tracers of atmospheric
motion. A separate analysis using Cassini’s visual and infrared mapping
spectrometer, led by Kevin Baines of JPL, confirmed the storm is very
violent, dredging up larger atmospheric particles and churning up
ammonia from deep in the atmosphere in volumes several times larger than
previous storms. Other Cassini scientists are studying the evolving
storm, and a more extensive picture will emerge soon.
The
Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. The mission is managed by JPL
for NASA’s Science Mission Directorate in Washington. The European
Southern Observatory in Garching, Germany operates the VLT in Chile. JPL
is a division of the California Institute of Technology in Pasadena.
For information about Cassini, visit: http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.
