Roederer Celebrates A 20-Year Space Odyssey

October 16, 1996

When the Galileo spacecraft shot into orbit around Jupiter last December, institute Professor Emeritus Juan Roederer celebrated a 20-year odyssey of his own.

In 1976, an international team working on the initial planning stages of the Galileo mission asked Roederer to join them. Because he is one of the world's leading researchers on Earth's radiation belts, they asked if Roederer would help them study the radiation belts circling Jupiter.

Twenty years later, Roederer will finally begin his long-awaited study of the belts around the solar system's largest planet. In June, he and other team members will review data from an energetic particle detector, one of about a dozen experiments aboard Galileo, which is now in an orbital path around Jupiter and eight of its 16 moons.

"The energetic particle detector works like a telescope," Roederer said. "It scans and sees the particles moving in Jupiter's radiation belts. We want to figure out where those particles come from, what they are made of, and how they get their energy."

Jupiter is a logical target for Roederer's research because it supports the fiercest, most intense radiation belts in the solar system. Radiation belts contain the most energetic particles of the magnetosphere, the plasma envelope composed of ultrahot particles that surrounds all planets with magnetic fields.

Jupiter's massive magnetosphere, by far the largest object in the solar system, extends up to 300,000 miles from the surface of the planet toward the sun. Solar wind continuously blowing around Jupiter's magnetosphere pushes the outlying particles back, causing the formation of a comet-like tail that stretches for millions and millions of miles.

Researchers plan to study many aspects of the magnetosphere, but Roederer is particularly interested in how Io, one of Jupiter's moons, affects the planet's radition belts. After sifting through data, he hopes to compare Jupiter's radiation belts to the Van Allen belts surrounding Earth.

"Earth's radiation belts are formed like the aurora," Roederer said. "Particles heated up in the tail of the magnetosphere are shot like a gun toward Earth. Some of them zip along magnetic field lines to create the aurora; other particles stay trapped, feeding Earth's radiation belts."
Scientists don't know if the same process is at work on Jupiter. Information about Jupiter's radiation belts and data from other Galileo experiments will help scientists understand more about how weather and activity in space affects Earth systems.

"The more we depend on satellites for so many uses, the more vulnerable we are to conditions in space," Roederer said. "Scientists hope someday to be able to predict weather in space the way forecasters predict weather on Earth."

Scientists obtained the first atmospheric data ever from the surface of any outer planet after Galileo dropped a 746-pound probe through the top of the cloudy, gaseous envelope surrounding Jupiter this winter.
According to NASA scientists, all instruments on the probe appeared to operate without a hitch after traveling for six years during Galileo's 2.3 billion-mile journey to Jupiter.

At the December meeting of the American Geophysical Union in San Francisco, scientists announced that the probe radioed data from Jupiter's turbulent upper atmosphere to Galileo for 57 minutes before contact was broken and the spacecraft fired its main thrusters to propel itself into orbit around the massive planet.

The success of the probe, the fastest manmade object ever to enter an atmosphere, was a boost to the Galileo mission, which has suffered some setbacks since it was approved by Congress in 1977.

For example, the spacecraft was ready in 1984, but after the explosion of the shuttle Challenger, Galileo's launch from a space shuttle was postponed until 1989.

Then its high-capacity main antenna failed to open properly, forcing scientists to find alternative methods to beam data home using a slow-rate antenna. More recently, the temporary malfunction of a tape recorder forced engineers to restrict its use so it could be dedicated fully to receiving data from the probe.

When the 1984 launch was delayed, scientists had an opportunity to update only certain aspects of the instrumentation aboard the spacecraft.

"We are dealing with data that is arriving in the middle of the 1990s derived from early 1980s technology," said Roederer, who estimates that Galileo would be one-fifth its size if modern electronics were aboard.

Regardless of how soon the data is analyzed, Roederer is sure to be associated with Galileo for a lifetime because his signature and those of other researchers are engraved on a plaque carried by the spacecraft.

Scientists estimate Galileo will orbit in space for at least 400 million years before it disintegrates under the intense bombardment of particles trapped in Jupiter's radiation belts.

"With a little luck, our signatures might even last more than a billion years," Roederer said. Now, that's a family legacy.

University of Alaska Fairbanks, Geophysical Institute

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