Probe Paints New Picture of Jupiter’s Magnetic Field : Astronomy: Ulysses survives a wild ride through the giant planet’s intense radiation belt. The magnetosphere extends about 5 million miles on one side, twice as far as expected.

Emerging unscathed from its wild ride through giant Jupiter’s intense radiation belt, the robot spacecraft Ulysses is painting a new, more complex picture of the vast magnetic field ringing the planet.

The field extends 5 million miles from the bright side of the planet, about twice as far as expected, and is also much flatter than astronomers had imagined, U.S. and European researchers announced Tuesday at the Jet Propulsion Laboratory in Pasadena. The field is thought to be even longer on the planet’s dark side.

“It’s a busy place,” said Michael Kaiser of the Goddard Space Flight Center, one of the principal investigators for the Jupiter fly-by.

The amount of energy in Jupiter’s magnetosphere, about 100 billion kilowatts, could supply all the power needs of the United States continuously.

Mysterious bursts of energy occur every 10 hours, and Ulysses found for the first time that the pulses are present throughout the entire magnetic field.

In addition, the craft taught researchers a great deal about the ionized gas “doughnut” that circles the planet, a result of the oxygen, sodium and sulfur spewed forth at about one ton per second from volcanoes on the Jovian moon Io. The gas is electrically charged by the magnetosphere’s radiation.

The yellowish doughnut, it turns out, has thin patches and thick spots, and overall was about half as dense as researchers expected, based on data sent from Voyager 1 and Voyager 2 in 1979. A slowing of volcanic activity on Io since then could be one explanation, though “we are not geologists,” cautioned Edward J. Smith, NASA’s project scientist for Ulysses.

The doughnut has “a definite wobble” because of the magnetic field, said Michael Bird, a researcher from Bonn University in Germany. The gases, heated to more than 12.2 million degrees Fahrenheit, travel at speeds of 260,000 miles per hour.

Ulysses carries no camera but relies instead on magnetic detectors and radio signals for exploration.

Over the next week, Ulysses will journey to Jupiter’s unexplored dark side, where researchers hope to find new information about the planet’s aurora, which is similar to the natural light displays over Earth. They also hope to study interplanetary dust.

Then, in the next few months, the sun’s gravity will take control and guide Ulysses to its primary research mission: an examination of the sun’s south pole in 1994 and its north pole in 1995. This will be the first look at the poles.

In order to achieve this polar orbit, Ulysses needed to use Jupiter’s immense gravity to propel the spacecraft out of the plane of the solar system’s planets.

The spacecraft, which was built by the European Space Agency and launched by the U.S. space shuttle Discovery in 1990, withstood heavy bombardment of radiation from about 6 p.m. Friday through about 7 a.m. Saturday, Smith said.

Scientists had feared that Jupiter’s radiation belt, one of the most dangerous regions in the solar system, might damage the craft, but “we passed through and survived the dragon’s den,” said John Simpson of the University of Chicago.

“Most happily, everything is in perfect working order,” said European Space Agency Project Manager Derek Eaton.

Ulysses’ Latest Encounter

The robot spacecraft Ulysses has emerged unscathed from its journey through one of the most dangerous regions in the solar system, the magnetic field of Jupiter. Ulysses used Jupiter’s immense gravity to push the spacecraft out of the orbit that planets take around the sun, in order to travel directly over the sun’s poles in 1994 and 1995.

Making its closest approach to Jupiter on Saturday, Ulysses found a magnetic field 5 million miles long. The field:

* Concentrates sulfur and oxygen emerging from volcanoes on Io, a moon of Jupiter, into a doughnut-shaped stream of ionized gases that orbits the planet.

* Contains enough energy to power the United States.

* Mysteriously pulses every 10 hours.