Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, December 25, 1994 TAG: 9412270070
SECTION: NATIONAL/INTERNATIONAL PAGE: A-20 EDITION: HOLIDAY
SOURCE: The New York Times
DATELINE: PASADENA, CALIF. LENGTH: Medium
It took the gravity of mighty Jupiter to bend the Ulysses spacecraft's trajectory ``downward'' and away from this plane of the ecliptic, sending it off where no craft had ever traveled. In observations over the last four months from this completely new perspective, the spacecraft has presented scientists with a wealth of data about solar dynamics and some findings that they did not expect, and have yet to understand.
``A number of longstanding questions have been answered, but, as usual, there have been major surprises,'' said Dr. Edward J. Smith, chief scientist for the $750 million Ulysses project at the Jet Propulsion Laboratory here, where it is being controlled. The project is a joint venture of the European Space Agency, which built the spacecraft, and the National Aeronautics and Space Administration.
Launched from a space shuttle in October 1990, the 800-pound Ulysses spacecraft last month completed the first survey of the Sun's southern polar region, passing over it at a distance more than twice as far from the Sun as the average distance from the Sun to Earth, or about185 million miles.
The two Voyager spacecraft, after exploring the outer planets, climbed out of the plane of the ecliptic and toward the edge of the planetary system. Scientists described the first survey results in interviews this month and in reports at a recent meeting of the American Geophysical Union in San Francisco.
The new findings concern magnetic fields, cosmic rays and solar winds, the electrically charged atomic particles that blow out from the Sun's outer atmosphere, or corona, in all directions and at great speeds.
The velocities of these winds, it has been observed, are twice as fast in the region out from the Sun's polar latitudes. The strength of the Sun's magnetic field over the poles is about the same as it is near the equator. And one of the biggest surprises involved cosmic rays, high-energy particles, ranging from hydrogen to uranium, that arrive from elsewhere in the galaxy, often from exploding stars. These particles were somewhat more dense near the solar poles, but not to the extent expected.
``The cosmic ray results were a total surprise,'' said Dr. Bruce E. Goldstein, the laboratory's deputy project scientist.
When the Sun is relatively quiet, as it is now, the cosmic-ray intensity should be at its peak. The Sun's magnetic fields are less powerful at the poles, and scientists thought that would allow perhaps 50 percent more cosmic rays to enter into the solar system there than near the Sun's equator and out along the plane of the ecliptic extending from the equator.
``Over the pole is where the field lines may connect into the interstellar medium, explained Dr. John A. Simpson, a University of Chicago physicist who is directing the mission's cosmic and solar particle investigation. ``They are like pipes channeling the lower-energy cosmic rays into the polar regions.''
But Ulysses data, which showed only slightly higher cosmic-ray intensities at the solar pole, seemed to be telling a more complicated story. Other instruments may be providing an explanation.
The spacecraft's magnetometers revealed strong wave-like variations in the Sun's magnetic fields in the polar region. A possible explanation for the magnetic waves, scientists suggested, is that the ends of the magnetic line of force attached to the Sun are being subjected to powerful churning motions of the Sun's surface. Evidence of such turbulence, resembling the motions seen in a bowl of porridge on a hot stove, has been observed from Earth.
Whatever their cause, the magnetic waves, Goldstein said, ``are just what is needed to scatter the cosmic rays, preventing many of them from getting in the solar system."
by CNB