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.

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.

“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.”

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 online from NASA’s Jet
Propulsion Laboratory, Pasadena, Calif., at
http://www.jpl.nasa.gov/videos/jupiter and from the Cassini
imaging science team’s site at http://ciclops.lpl.arizona.edu

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. “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.

“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.

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.

“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.”

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.

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.” At the planet’s surface, one
would see only east and west winds, alternating with latitude
and symmetric about the equator. “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.

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. 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.

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.

More information about the Cassini-Huygens mission is
available online at http://www.jpl.nasa.gov/cassini/ . The
mission is a collaboration of NASA, the European Space Agency
and the Italian Space Agency. JPL, a division of Caltech,
manages the Cassini program for NASA’s Office of Space
Science, Washington, D.C.


NOTE TO BROADCASTERS: A video file with the Jupiter movie
sequences and B-roll will air on July 17 at noon EDT. NASA
Television is available at GE-2, Transponder 9C at 85 degrees
West longitude, with vertical polarization. Frequency is on
3880.0 megahertz with audio on 6.8 megahertz.