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Spacecrafts Shed Light on
Jupiter
By RICK
CALLAHAN
.c The Associated
Press
Astronomers probing the vast northern lights that ring Jupiter's north pole
have found a mysterious X-ray ``hot spot'' that flares up like a beacon every
45 minutes.
Scientists said it could take years to explain this pulsating region, which
its discoverers speculate may be related to bursts of radio waves that emanate
from the giant planet at a similar interval.
``It came as a complete surprise, but scientists live for that. Sometimes
the things that are most unexpected are the most important,'' said Christopher
Russell, a University of California, Los Angeles professor of geophysics.
Russell was not involved in the research.
The discovery of the hot spot is one of several surprises that have emerged
from a unique opportunity scientists had last year to study Jupiter and the
enormous magnetic cocoon that surrounds it.
The occasion was a space science first - the first time two spacecraft had
visited Jupiter, or any outer planet, at the same time.
In early January 2001, the Galileo orbiter that has been circling Jupiter
since 1995 and the Cassini probe, which swung past Jupiter on its way to
Saturn, passed through Jupiter's magnetosphere - a zone of magnetically charged
particles trapped within its magnetic field.
Images taken during the same period by the Hubble space telescope and the
Chandra X-Ray Observatory, both in orbit around the Earth, complemented the
spacecraft's observations.
Seven papers that arose from that data were highlighted in the Feb. 28 issue
of the journal Nature, describing various aspects of Jupiter's magnetosphere
and its interaction with the planet's upper atmosphere.
The data transmitted back showed, as scientists had predicted, that Jupiter's
magnetosphere changes shape as it is buffeted by interplanetary shock waves
created by the solar wind - the stream of particles thrown off by the sun.
Earth's magnetosphere acts similarly.
But Jupiter's is more complex and far larger. At about 100 times as wide
as the planet, it's so large that if it were visible to the naked eye, it
would appear larger than the full moon to an observer on Earth. And its cometlike
tail extends past the orbit of Saturn.
Randy Gladstone, a planetary scientist at the Southwest Research Institute
in San Antonio who was lead author on the X-ray hot spot paper, said his
team is still in the early stages of trying to figure out what is causing
the pulsating spot.
He said the disturbance accounts for most of the X-ray emissions that are
seen in Jupiter's northern auroras. Scientists had thought those emissions
were produced by sulfur and oxygen ions blasted into space by Jupiter's volcanic
moon, Io, and then energized by circulating through the Jovian magnetic field.
Now, it's not clear what is behind those emissions, Gladstone said. The evidence
points to an origin much farther away from Jupiter, near the edge of its
magnetosphere, where it meets the solar wind.
``Something is causing these emissions - from X-rays to ultraviolet to radio
(waves). There's something connecting all of these emissions to have them
happen over all these wavelengths,'' Gladstone said.
John Clarke, a professor of astronomy at Boston University, and colleagues
authored another paper that reported the discovery of a ghostly glowing trail
etched by Io into Jupiter's ionosphere, the region high in its atmosphere
where auroras form.
His team also found that two of Jupiter's three other large moons - Ganymede
and Europa - etch smaller, oval ``magnetic footprints.''
Scientists already knew Io, the most volcanically active body known in the
solar system, was producing a similar footprint.
But Clarke said that since Europa and Ganymede do not have volcanoes but
still produce footprints in Jupiter's ionosphere, it appears some unknown
mechanism is causing all three moons to leave their mark there.
Jupiter's fourth large moon, Callisto, may cast such a spot, too. But whether
it does may remain unanswered for years to come because no new missions to
Jupiter are planned, and the Galileo spacecraft will end with a fiery plunge
into Jupiter next year.
A proposed spacecraft that would be the first to visit Pluto, the outermost
planet, would swing by Jupiter on its decade-long journey, giving it a chance
to study the planet. But that mission's funding remains in question.
On the Net:
X-ray spot animation:
http://pluto.space.swri.edu/yosemite/jupiter/chandra-hrc.html
Nature: http://nature.com
AP-NY-03-10-02
1202EST
Copyright 2002 The Associated Press. The information
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Researcher Steven L. Wilson, Sr