May 19, 2011

Giant Storm Revealed On Saturn

NASA's Cassini spacecraft has revealed a giant early-spring storm in Saturn's northern hemisphere that is so powerful it stretches around the entire planet.

NASA said on Thursday that the storm has been wrecking havoc for months and shooting plumes of gas high into the planet's atmosphere.

Cassini's radio and plasma wave science instruments first detected the large disturbance, and amateur astronomers tracked its emergency in December 2010, according to the space agency.

NASA said the storm produced a 3,000-mile-wide dark vortex, similar to Jupiter's Great Red Spot, within the turbulent atmosphere.

The deep plumes generate regions of warm air that shine bight "beacons" of infrared.

"Nothing on Earth comes close to this powerful storm," Leigh Fletcher, the study's lead author and a Cassini team scientist at the University of Oxford in the United Kingdom, said in a statement. "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.

"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," Glenn Orton, a paper co-author, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif, said in a statement.

NASA said the violence of the storm took researchers by surprise because it was the strongest disturbances ever detected in Saturn's stratosphere. 

"On Earth, the lower stratosphere is where commercial airplanes generally fly to avoid storms which can cause turbulence," 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, said in a statement.

"If you were flying in an airplane on Saturn, this storm would reach so high up, it would probably be impossible to avoid it."

Cassini's composite infrared spectrometer (CIRS) found evidence of the storm's strength 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 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 storm.  Details of the discovery are published in Science.


Image 1: Thermal infrared images of Saturn from the Very Large Telescope Imager and Spectrometer for the mid-Infrared (VISIR) instrument on the European Southern Observatory's Very Large Telescope, on Cerro Paranal, Chile, appear at center and on the right. An amateur visible-light image from Trevor Barry, of Broken Hill, Australia, appears on the left. The images were obtained on Jan. 19, 2011, during the mature phase of the northern storm. The second image is taken at a wavelength that reveals the structures in Saturn's lower atmosphere, showing the churning storm clouds and the central cooler vortex. The third image is sensitive to much higher altitudes in Saturn's normally peaceful stratosphere, where we see the unexpected beacons of infrared emission flanking the central cool region over the storm. Credit: ESO/Univ. of Oxford/T. Barry

Image 2: This false-color infrared image, obtained by NASA's Cassini spacecraft, shows clouds of large ammonia ice particles dredged up by a powerful storm in Saturn's northern hemisphere. Credit: NASA/JPL/Univ. of Arizona

Image 3: Measurements by NASA's Cassini spacecraft reveal temperatures in a high layer of Saturn's atmosphere known as the stratosphere and show the dramatic effects of the massive storm deep below. Credit: NASA/JPL/GSFC/Univ. Oxford


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