Rising Storms Revise Story of Jupiter's Stripes
Jet Propulsion Laboratory, Pasadena, Calif.
Southwest Research Institute, San Antonio
|March 6, 2003
This image of Jupiter was taken by
NASA's Cassini spacecraft. The Great Red Spot (below and to the
right of center) is a giant atmospheric storm as wide as two Earths
and over 300 years old, with peripheral winds of 483 kilometers
per hour (300 miles per hour).
Pictures of Jupiter, taken by a NASA spacecraft on its way to Saturn,
are flipping at least one long-standing notion about Jupiter upside
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,
"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:
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