- PASADENA - A kaleidoscopic
movie made from about 1,200 Jupiter images taken by NASA's Cassini spacecraft
reveals unexpectedly persistent polar weather patterns on the giant planet.
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- Long-lived storms and globe-circling belts of clouds
are familiar features around Jupiter's midsection, easily seen even in
still pictures. Closer to the poles, though, still images show widespread
mottling that appears chaotic.
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- "You'd expect chaotic motions to go with the chaotic
appearance, but that's not what we see," said the planetary scientist
who put the movie together, Dr. Ashwin Vasavada of the California Institute
of Technology, Pasadena. "The movie shows that the small spots last
a long time and move in organized patterns."
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- Cassini shot the images in infrared light to cut through
Jupiter's upper haze and show the clouds underneath in black and white.
The movie clip combines those images taken over a span of 70 days into
a sequence less than a minute long. The version centered on the north pole
and another version showing the entire planet are available http://ciclops.lpl.arizona.edu
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- Caltech planetary scientist Dr. Andrew Ingersoll, a member
of the Cassini imaging team, said the movie also gives insight into storms'
duration in Jupiter's high latitudes. "There are thousands of storms
there the size of the biggest storms on Earth," he said.
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- "Until now, we didn't know the lifetime of those
storms." The movie shows thousands of spots bumping into each other
but generally moving together within each band of latitude. The spots occasionally
change bands or merge with each other, but usually they last for the entire
70 days. Each spot is an active storm in Jupiter's atmosphere.
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- "The smaller and more numerous storms at high latitude
share many of the properties of their larger cousins like the Great Red
Spot at lower latitudes," Ingersoll said.
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- The mystery of Jupiter's weather is why the storms last
so long. Storms on Earth last a week before they break up and are replaced
by other storms. The new data heighten the mystery because they show long-lived
storms at the highest latitudes, where the weather patterns are more disorganized
than at low latitudes.
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- "Perhaps we should turn the question around and
ask why the storms on Earth are so short lived," Ingersoll said. "We
have the most unpredictable weather in the solar system, and we don't know
why."
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- Dr. Carolyn Porco, Cassini imaging team leader and a
planetary scientist at the Boulder, Colo., office of Southwest Research
Institute, presented the movie at a meeting of Jupiter scientists in Boulder
recently. "This is the first movie ever made of the motions of Jupiter's
clouds near the poles, and it seems to indicate that one notion concerning
the nature of the circulation on Jupiter is incomplete at best, and possibly
wrong," she said.
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- The model in question suggests that Jupiter's alternating
bands of east-west winds are the exposed edges of deeper, closely-packed
rotating cylinders that extend north-south through the planet. In this
laboratory-tested model, Porco said, "many such cylinders sit side-by-side,
girdling the planet like rings of narrow solid-rockets strapped to the
outside of a larger rocket."
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- At the planet's surface, one would see only east and
west winds, alternating with latitude and symmetric about the equator.
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- "However, the east-west winds that the movie shows
in the polar regions don't fit that model," Porco said. Jupiter's
wind pattern may involve a mix of rotation-on-cylinders near the equator
and some other circulation mechanism near the poles.
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- The movie required processing of images that Cassini
took through an infrared filter during the last three months of 2000. The
position of the spacecraft slightly north of the planet's equatorial plane
gave an oblique view of Jupiter's north pole.
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- The images were projected into maps of the northern hemisphere
as if viewed from directly above the pole. In that view, the high-latitude
mottling becomes a concentric series of circular bands, each rotating in
the opposite direction as adjacent bands.
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- Cassini, launched in 1997, passed Jupiter on Dec. 30,
2000, on its way toward its ultimate destination, Saturn. It will begin
orbiting Saturn on July 1, 2004, and drop its piggybacked Huygens probe
onto the haze-wrapped moon Titan about six months later.
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- Working the problem has been a keystone of the space
program for decades. Whatever the cause of a problem, if at all possible,
a solution must be found. And for the past year a deep space mission team
has been working to solve a communication problem that will happen in 2004
when for a few hours two spacecraft communicate as they set about exploring
Sol's biggest lightweight Titan during the first phase of Cassini's four-year
mission to Saturn.
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