Galileo plowing through dust storm

The Associated Press

LOS ANGELES The unmanned Galileo spacecraft heading for Jupiter is plowing through a dust storm, the heaviest it has encountered on its interplanetary voyage.

Scientists aren't sure whether the electrically charged dust comes from a volcano on Jupiter's moon Io, from particle rings that circle the giant planet or from the Comet Shoemaker-Levy 9, which crashed into Jupiter's cloudy atmosphere last year.

But they're excited at the prospect of getting answers.

''Finding a source of dust like this coming out of Jupiter, with Jupiter acting like a big electromagnetic accelerator spewing dust into the solar system, is a completely unanticipated discovery,'' Torrence Johnson, Galileo project scientist at NASA's Jet Propulsion Laboratory in Pasadena, said Tuesday.

''We are hoping to be able to pinpoint the source once we get into Jupiter's system,'' said Carol Polanskey, JPL's team chief for dust detection.

The storm wouldn't count for much on Earth. Instruments are detecting only about 20,000 tiny particles per day, said Eberhard Grun of Germany's Max Planck Institute for Nuclear Physics. But that compares with a typical rate of only about one particle every three days on the voyage.

Galileo, which was launched in 1989 aboard a space shuttle, first began observing dust from Jupiter in June 1994. It has run into several dust storms since December 1994, each typically lasting a few days. But the latest, which began on July 28, is the greatest so far.

The spacecraft is now 39 million miles away from the planet. When it enters Jupiter's orbit in December, Earth will be 560 million miles away.

Galileo's atmospheric probe, which separated from the main orbiter on July 13th, is set to enter Jupiter's dense clouds on Dec. 7, when it will relay atmospheric information to the main spacecraft. Although the cone-shaped probe is expected to be destroyed by the planet's dense atmosphere, the main spacecraft will begin a two-year, 11-orbit survey of the planet and its many moons.

The $1.6 billion Galileo mission is a joint U.S.-German venture.

The German-built dust detector is about the size of a large kitchen colander. By counting the number of particles that touch its gold-plated detector area and recording their direction and energy, the instrument provides sufficient information for scientists to estimate the size and speed of the particles.

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