Solar Probe Catches New Waves From Sun's Core
Joint European-American space probe Ulysses feels its way around the sun to discover the boundaries of the star's influence. The probe's mission involves both the wonder of scientific discovery and the search to better understand practical effects of solar activity
ULYSSES - the probe that's gone where no spacecraft has been before - is giving scientists a new perspective on our solar system. It may also give them a glimpse of what's going on in the sun's energy-producing core.Skip to next paragraph
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That's not bad for a space probe that can't even see what it's doing.
Ulysses has no imaging equipment, explains Edward Smith, Ulysses project scientist at the California Institute of Technology's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. But, he adds, ''we've learned a lot of really interesting things'' as the spacecraft feels, listens, and tastes its way through unexplored regions high above the sun's poles.
Cameras wouldn't do scientists any good as they try to understand what's going on in the bulk of our solar system. Most of it is invisible. Ulysses' detectors are just what's needed to chart the tangle of magnetic fields and outward rushing solar winds of electrically charged particles that fill a seemingly empty void. Its sensors trace out the magnetic force patterns the probe encounters. They listen for the ''ping'' of small dust particles. They discriminate among different chemical elements to list the ingredients in the solar wind.
It is the outward push of that wind and the deflecting force of the magnetic fields that set the boundaries of the solar system - not the planets, moons, and other solid bodies. This seemingly ethereal interplanetary medium determines where the sun's sphere of influence ends and interstellar space begins.
Before Ulysses, space probes had sampled only a small part of that medium in regions near the plane of the sun's equator where the planets orbit. Now Ulysses is enabling scientists to study it in a way that was impossible before, by giving them a three-dimensional view.
To reach stations over the solar poles, Ulysses had to turn out of the plane of the sun's equator. No available rocket was powerful enough to launch it on such a course. Instead, Ulysses headed for Jupiter, arriving Feb. 11, 1992. The giant planet's gravity flung it into its final orbit.
The main exploration began last fall as the spacecraft moved toward the region over the sun's south pole. On Sept. 13, it reached 80.22 degrees south solar latitude. Then it swung back up, crossing the solar equator again March 12. And yesterday, it reached its highest point at north latitude 80.2 degrees.
In late September, Ulysses will head back out to Jupiter's orbit. It will return to the sun in the year 2000, just in time to make a second set of observations as the sun, which is now quiescent, enters a new active phase as part of the normal sun-spot cycle.
Looking inside the sun
Ulysses never came closer to the sun than 1.34 times Earth's average distance away. Indeed, it wasn't designed to study the sun at all. That's why Dr. Smith calls it ''truly astounding'' that the most recently reported findings seem to reveal processes deep within the solar interior.
Last month, statisticians Louis Lanzerotti, Carol Maclennan, and David Thomson reported in the journal Nature that they have found signs of waves from within the sun's core impressed on magnetic field lines and on the solar wind spewing outward far beyond the sun's surface. Solar physicists have been looking unsuccessfully for signs of such waves on the sun itself.
They have seen plenty of oscillations made by sound waves. But these deep solar waves are gravity waves, like waves on water. The Bell Labs team has finally found them in Ulysses data and in data gathered by the Voyager 2 spacecraft in 1985.