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NASA craft shows Jupiter's huge, old storms raging,

NASA craft shows Jupiter's huge, old storms raging

By Kevin Krolicki

PASADENA, Calif., Dec 30 (Reuters) - NASA's Cassini spacecraft has swung through its closest approach to Jupiter, capturing dramatic movies of the birth and death of the fierce storms that rage across the planet's surface, scientists said on Saturday.

The new images of thunderstorms swirling across the solar system's largest planet suggest that the massive storms, which can run for centuries, draw their energy from absorbing smaller systems, Andrew Ingersoll of the California Institute of Technology said.

Jupiter's famous Great Red Spot, visible with a telescope, is thought to be a 300-year-old thunderstorm packing 300-mph (480-kph) winds across an area three times as wide as Earth.

The new images captured by Cassini, which packs a camera with filters that allow it to peer deep into Jupiter's cloud cover, show what appear to be smaller, white storms being created, absorbed by larger systems around the Red Spot and then torn apart as they stray into a shear zone created by pressure differentials, Ingersoll said.

Previous observations from the U.S. space agency's Galileo spacecraft, orbiting Jupiter since 1995, have suggested that smaller thunderstorms draw their power from below the cloudy surface of the hot, gassy planet.

A MORE NEARLY PERFECT STORM

"The weather is different on Jupiter. You have a 300-year-old storm. We'd like to know why Jupiter's weather is so stable and Earth's is so transient," he said at a news conference at NASA's Jet Propulsion Laboratory.

New and old color photographs and movies of Jovian weather are on the Web at http:/www.jpl.nasa.gov/pictures/jupiter.

Galileo has surprised the National Aeronautics and Space Administration by remaining operational as long as it has. Scientists are also using data from it and Cassini to study how the solar wind of particles speeding away from the sun affects the huge magnetic region surrounding Jupiter.

"For the first time we have the opportunity to have a weather station in the solar wind," William Kurth of the University of Iowa said.

One immediate finding was that the huge bubble of charged particles known as Jupiter's magnetosphere is changing size more rapidly than expected.

Cassini hit Jupiter's magnetic boundary on Thursday, Kurth said, much farther out than anticipated, recording a burst of radio waves similar to the sonic boom created by a jet breaking the sound barrier.

Earlier this fall, Galileo had broken through Jupiter's magnetic boundary only to have the bubble collapse suddenly and unexpectedly back toward the planet, Kurth said.

RESULTS OF IO'S VOLCANOES

Cassini, which passed within 6 million miles (9.7 million km) of Jupiter on Saturday, has also collected evidence of a huge nebula of volcanic material surrounding the planet, scientists said. This has been spewed out by Io, one of its four largest moons, they said.

Cassini, one of the heaviest and most complex spacecraft ever launched, ran into some trouble in mid-December after registering unusual drag on one of the electric wheels that point the craft and its instruments.

The flight team was able to restart the so-called grinding wheel on Dec. 21 but have suspended operations that require turning the spacecraft to conserve fuel.

Cassini, launched in 1997, is bound for Saturn, where it is scheduled to swing into orbit inside the outermost ring and dispatch a European-built, parachute-equipped probe to the planet's largest moon, Titan.

Haze-shrouded Titan is thought to have an atmosphere much like Earth's, but with clouds, rain and weather patterns produced by methane gas.

The main purpose of Cassini's approach to Jupiter was to give the 12,593-pound (5,712-kg) spacecraft a final gravitational push toward Saturn, where it is expected to arrive on July 1, 2004.

20:55 12-30-00

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