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Jupiter and Io: infrared spots mark link.

Astronomers have discovered a pair of ghostly spotlights that sweep across Jupiter in synch with the motion of its moon Io. Reseachers say the faint infrared emissions, detected at NASA's Infrared Telescope Facility atop Hawaii's Manua Kea, stem from the interplay between Io and the magnetic field of Jupiter

Researchers have long suspecte that Io and Juipter influence each other through an elecrical interaction in which magnetic field lines from the planet strike the moon, notes John E.P. Connerney of NASA's Goddard Space Flight Center in Greenbelt, Md. But scientists hadn't located the exact places in Jupiter's polar regions form which the magnetic field lines enter and exit the planet.

In marking the two magnetic foot-prints, the infrared spots "provide a magnetic road map of the planet," Connerney says.

He and Richard Baron, Takehiko Satoh, and Tobias C. Owen of the University of Hawaii in Honolulu, reported their study in the Nov. 12 SCIENCE.

The finding, says Connerney, upholds a theory proposed in 1969 that Jupiter's rotating magnetic field acts as an electrical generator on Io, inducing a voltage across the moon. The voltage creates 5 million amperes of current that flow back to Jupiter through two separate circuits-magnetic field lines that originate form its north and south polar regions. The infrared emissions might stem from the electrical heating generated by the current, he says.

Alternatively, Connerney adds, as the flow of electrons in the current crashes into Jupiter's ionosphere, it may excite ions there to glow in the infrared. In either case, the interaction appears the likely cause of variations in the raido signals emitted by hte planet.

Both infrared spots remain about 8 degrees closer to the equator than the luminous polar patches associated with Jupiter's aurora, indicating that Io plays no major role in generating this electromagnetic disturbance, Connerney says.

Alexander J. Dessler of the University of Arizona in Tucson says the study indicates that magnetic maps of Jupiter generated form Voyager data are more accurate than those form Pioneer 141. Tracking the motion of the spots, he adds, will provide a sensitive test of whether Jupiter reverses its magnetic field every decade or so, like the sun, or roughly every half million years, like earth.
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Title Annotation:infrared emissions resulting from interaction between Jupiter's magnetic field and moon
Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:Nov 20, 1993
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