Scientists have found evidence for a new ring of dust that occupies a backward orbit around Jupiter, based on computer simulations and data from NASA's Galileo spacecraft, it is reported in today's issue of Science magazine.

A team led by researchers at the University of Colorado at Boulder reported that a faint, doughnut-shaped ring of interplanetary and interstellar dust some 1,126,000 kilometers in diameter (about 700,000 miles) appears to be orbiting the giant planet. Evidence for the new ring's existence comes from computer simulations that correlate with data collected by a dust detector aboard the Galileo spacecraft has detected this ring by capturing some of its dust, said Dr. Joshua Colwell, a research associate at the university's Laboratory for Atmospheric and Space Physics.

Surprisingly, the researchers say, most of the interstellar and interplanetary dust particles appear to be in a "retrograde" orbit -- that is, moving in the opposite direction of the rotating planet and its moons, Colwell said. The reason for the backward orbit of the tiny particles is not yet clear, he said.

The paper in Science magazine was authored by Colwell, research associate Dr. Mihaly Horanyi, also of the Laboratory for Atmospheric and Space Physics, and planetary scientist Dr. Eberhard Grun of the Max Planck Institute for Astrophysics in Heidelberg, Germany, who is the principal investigator on Galileo's dust detector.

The Galileo mission is managed by NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. JPL is a division of the California Institute of Technology, Pasadena, CA.

NASA's Voyager 2 detected an uneven dust ring around Jupiter in 1979 that scientists believe was created by the collisions of small moonlets with micrometeoroids in the Jovian system. But the newly identified ring of dust with smoke-size particles originating from beyond the Jovian system appears to be much larger, more sparse and, possibly unique in the solar system.

"I suspect we may wind up seeing something similar at Saturn," said Colwell. Launched in 1997, NASA's Cassini spacecraft will reach the ringed planet in 2004.

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