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Release: Jan. 2, 2001

UI researchers use two spacecraft to explore Jovian magnetosphere

IOWA CITY, Iowa -- When it comes to studying the magnetosphere of Jupiter during the next several weeks, two spacecraft are better than one.

That's the message University of Iowa research scientist William Kurth delivered at a recent news conference at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Kurth, who serves as co-investigator for the UI plasma wave instrument on the Galileo spacecraft that has orbited Jupiter for the past five years, is also deputy principal investigator for the UI plasma wave instrument on board the Cassini spacecraft. Cassini currently is swinging past Jupiter after having made its closest approach to the planet Dec. 30.

"For the first time, we have the opportunity to use two spacecraft to study Jupiter at the same time at close range," he says. "We want to understand to what extent the solar wind affects the magnetosphere of Jupiter." Previous measurements made by the Voyager spacecraft indicated that the solar wind, a hot, ionized gas flowing outward from the Sun, has some effect on Jupiter's magnetosphere, a huge region of electrically charged particles and magnetic fields surrounding the planet.

"We hope to use measurements of the solar wind being made by Cassini in conjunction with the Galileo measurements within Jupiter's magnetosphere. I suspect that some temporal variations are due to the solar wind. But it is also likely that some variations are related to changes in the amount of volcanic activity on Jupiter's moon, Io," says Kurth, whose colleague and principal investigator on both spacecraft is UI space physicist Donald Gurnett.

Scientists are interested in studying Jupiter and its magnetosphere, in part, because it resembles a smaller version of the solar system and, as such, offers an opportunity to learn about the evolution of the solar system. With a magnetosphere about 10 times stronger than the Earth's, Jupiter, like the sun, emits radio waves. The magnetic fields surrounding Jupiter are many times the size of the planet and, if visible, would rival the full moon in size on a clear night.

Kurth describes Cassini's flyby of Jupiter as "leisurely" because it came no closer to Jupiter than about 140 Jovian radii (some six million miles) compared to about seven radii for Galileo. As a result of Cassini being in the "neighborhood" for an extended time, scientists will continue to gather experimental data for several weeks.

Summarizing the investigation, Kurth says that the instrument on board Cassini is very advanced and is working very well. He added that recent data showed Cassini crossing Jupiter's bow shock, the outer limits of the magnetosphere, early on Dec. 28.

"We'll make the most comprehensive characterization of radio emissions from Jupiter ever made," he says. "As for Galileo, it's the 'little spacecraft that could.' We're all pleasantly surprised it's still working after receiving several times its designed radiation dosage."

In addition to Kurth and Gurnett, University of Iowa operations personnel commanding the Cassini radio and plasma wave instrument from Iowa City include: Terry Averkamp, George Hospodarsky, Ann Persoon and Bill Robison.

Launched in 1997, Cassini is a joint U.S. and European mission scheduled to begin a four-year investigation of Saturn and Titan, its largest moon, in July 2004.