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Donald Savage
Headquarters, Washington          March 6, 2003
(Phone: 202/358-1547)

Guy Webster 
Jet Propulsion Laboratory, Pasadena, Calif.  
(Phone: 818/354-6278)

Maria Martinez 
Southwest Research Institute, San Antonio
(Phone: 210/522-3305)

RELEASE: 03-95

RISING STORMS REVISE STORY OF JUPITER'S STRIPES

     Pictures of Jupiter, taken by a NASA spacecraft on its way to 
Saturn, are flipping at least one long-standing notion about Jupiter 
upside down.

Stripes dominate Jupiter's appearance. Darker "belts" alternate with 
lighter "zones." Scientists have long considered the zones, with their 
pale clouds, to be areas of upwelling atmosphere, partly because many 
clouds on Earth form where air is rising. On the principle of what 
goes up must come down, the dark belts have been viewed as areas where 
air generally descends.

However, pictures from the Cassini spacecraft show that individual 
storm cells of upwelling bright-white clouds, too small to see from 
Earth, pop up almost without exception in the dark belts. Earlier 
spacecraft had hinted so, but not with the overwhelming evidence 
provided by the new images of 43 different storms. 

"We have a clear picture emerging that the belts must be the areas of 
net-rising atmospheric motion on Jupiter, with the implication that 
the net motion in the zones has to be sinking," said Dr. Tony Del 
Genio, an atmospheric scientist at NASA's Goddard Institute for Space 
Studies, New York. "It's the opposite of expectations for the past 50 
years," he said.

Del Genio is one of 24 co-authors from America and Europe reporting 
diverse results from the Cassini imaging of Jupiter in Friday's 
edition of the journal Science. Cassini's camera took about 26,000 
images of Jupiter, its moons and its faint rings over a six-month 
period as the spacecraft passed nearby two years ago.

"The range of illumination angles at which Cassini viewed Jupiter's 
main ring gives insight about particles in the ring by the way they 
scatter sunlight. The particles appear to be irregularly shaped, not 
spheres," said camera-team leader Dr. Carolyn Porco of Southwest 
Research Institute, Boulder, Colo. "They likely come from surfaces of 
one or more moons being eroded by micrometeoroid impacts," she said.

Spherical particles would suggest an origin as melted droplets, not 
erosion. In addition, Cassini imaging shows the degree to which the 
orbits of two small moons near the ring, Metis and Adrastea, are 
inclined matches the vertical thickness of the ring. That points to 
those moons as sources of the ring particles said Porco.

One surprise in ultraviolet images of Jupiter's north polar region is 
a swirling dark oval of high-atmosphere haze the size of the planet's 
famous Great Red Spot. "It's a phenomenon we haven't seen before, so 
it gives us new information about how stratospheric circulation 
works," said Dr. Robert West of NASA's Jet Propulsion Laboratory 
(JPL), Pasadena, Calif. The results show the winds and the life cycle 
of clouds in the stratosphere.

Also, movies of infrared images reveal persistent bands of 
globe-circling winds extend north of the conspicuous dark and light 
stripes. "The planet's appearance at high latitudes is like leopard 
spots, but when you see it in motion, it's interesting that all the 
spots at one latitude move in one direction and all the spots at 
adjacent latitudes move the opposite direction," said Dr. Andrew 
Ingersoll of the California Institute of Technology (Caltech), 
Pasadena.

Other discoveries reported include atmospheric glows of the large 
moons Io and Europa during eclipses, a volcanic plume over Io's north 
polar region, and the irregular shape of a small outer moon, Himalia.

"The Jupiter results provide some hints of the spectacular new 
findings that await Cassini when it reaches Saturn," Dr. Larry 
Esposito of the University of Colorado, Boulder, principal 
investigator for Cassini's ultraviolet-imaging spectrograph 
instrument, predicts in a separate commentary in Science about the 
Cassini camera results at Jupiter. Cassini will begin orbiting Saturn 
July 1, 2004, and will release its piggybacked Huygens probe about six 
months later for descent through the atmosphere of the moon Titan.

Cassini is a cooperative venture of NASA, the European and Italian 
Space Agencies. JPL manages it for NASA's Office of Space Science, 
Washington. Other co-authors include scientists from Cornell 
University, Ithaca, N.Y.; Free University of Berlin, Germany; Queen 
Mary, University of London, United Kingdom; University of Arizona, 
Tucson; University of Paris, France; German Aerospace Center, Berlin;
and University of California, Los Angeles.  

Images and mission information are available on the Internet at:

http://saturn.jpl.nasa.gov/gallery/jupiter-flyby/index.cfm, 
and

http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html 

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