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JPL Radio Observations of Comet Shoemaker-Levy


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Contact: James H. Wilson


Radio astronomers at NASA's Jet Propulsion Laboratory were surprised by an unexpectedly great increase in Jupiter's microwave emissions apparently associated with the bombardment of the planet by the fragmented Comet Shoemaker-Levy 9.

Dr. Michael J. Klein reports that the increase in radio intensity began soon after July 16 and peaked July 23 when the intensity was 25 percent greater than it had been before the comet encounter. It has been slowly fading each day since July 23, but is still much higher than normal.

"Although some researchers anticipated changes in Jupiter's radio output during the comet impacts, this powerful increase was unlike anything predicted before the events," Klein said.

The increase was apparent on July 21 when data taken at 2295 Megahertz with a 34-meter-diameter (112-foot) R&D antenna at Goldstone, California, were analyzed, he added. Astronomers in Australia have reported a similar increase in radio emissions, but at much longer wavelengths.

The research is part of the NASA/JPL Jupiter Patrol, a long-term radio astronomy monitoring program begun in 1971 and intensified in January 1994 in response to predictions of the cometary impacts in July. "We've never seen anything like this in the 23 years of the program," Klein said. "It's a big surprise."

Goldstone is one of three sites used by the NASA/JPL Deep Space Network to communicate with distant spacecraft such as Voyager and Galileo, but its giant dish antennas are frequently used as sensitive radio telescopes.

JPL radio astronomers are cooperating with a worldwide community of observers coordinated by Dr. Imke dePater of the University of California, Berkeley, which used such instruments as the 64-meter (210-foot) Parkes Telescope in Australia, the 43- meter (140-foot) National Radio Astronomy Observatory in Greenbank, West Va., the NRAO 27-antenna Very Large Array in New Mexico, the Naval Research Laboratory's instrument near Washington, D.C., and telescopes in the Netherlands and Germany.

Klein added that radio emissions from Jupiter originate from the giant planet's atmosphere and from its ring-like belts of charged particles, similar to Earth's Van Allen belts.

Dr. Samuel Gulkis, Klein's colleague in the Jupiter patrol, suggested that the impacting comet or the ensuing explosions may have enhanced Jupiter's belt of energetic electrons, circling the planet and trapped by its magnetic field.

"The interesting question is how the interaction of the comet with Jupiter accelerates the electrons to relativistic speed and traps them, at least temporarily, in the planetary magnetic field," Gulkis said. "The answers may provide a better insight on how the Sun produces its intense bursts of radio energy which sometimes interfere with communications on Earth."

The Jupiter Patrol is operated and managed by JPL for NASA's Office of Space Science and Office of Space Communication.

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