After a journey of more than 3 billion kilometers (2 billion miles), the Ulysses spacecraft has completed the first pole-to-pole passage over the Sun, showing scientists some of the solar forces at work in high latitude regions never before explored.
Scientists on the international NASA/European Space Agency mission gathered at Dana Point, CA this week for a 2-1/2-day workshop at which they compared notes on results from the spacecraft's first complete solar orbit and presented preliminary results of Ulysses' recently completed pass over the Sun's northern pole.
"This has been an exceptional journey to explore regions of the Sun never visited by spacecraft before," said Willis Meeks, U.S. project manager at NASA's Jet Propulsion Laboratory. "Spacecraft data over the polar regions of the Sun are allowing scientists to begin assembling the first three-dimensional picture of the heliosphere ever compiled."
Several scientists from the Ulysses team explained the mission's results in a panel discussion that aired today on NASA Television. They included Dr. Edward J. Smith, U.S. project scientist at JPL and a co-investigator on the magnetic fields experiment; Dr. John Phillips of Los Alamos National Laboratory, principal investigator on the solar wind plasma experiment; Dr. Antoinette Galvin, University of Maryland, a co-investigator on Ulysses who also works with x-ray images of the Sun from the Japanese Yohkoh mission; Dr. Richard Marsden, ESA project scientist and a co-investigator on the cosmic rays and solar particles experiment; and Dr. J. R. Jokipii, an interdisciplinary scientist from the University of Arizona.
Over the course of its five-year journey, Ulysses confirmed some theories about the Sun and found a few surprises, the scientists reported:
-- Ulysses verified global differences in solar wind velocity, composition and temperature.
-- The spacecraft saw outward-propagating, high-speed and long-period Alfven waves continuously in the high-speed solar wind over both poles of the Sun. (Alfven waves are waves which move along magnetic field lines and accelerate charged particles.)
-- An increase in magnetic field intensity in the polar regions was not seen, as was expected. Instead, Ulysses found a uniform magnetic field whose intensity did not change from equator to pole.
-- The theoretical "cosmic ray funnel," which would allow easy access of cosmic ray particles into the polar region, was not found. Only a slight increase in cosmic ray intensity was seen over the pole.
With its northern pass completed, Ulysses will begin to journey back out to the orbit of Jupiter. The spacecraft will reach the giant planet's distance of 5.4 astronomical units (about 800 million kilometers or 500 million miles) on April 17, 1998. Once there Ulysses will loop back and return, this time arriving in the vicinity of the Sun during its most active sunspot phase.
"The Sun will be near solar maximum in the fall of 2000 and the solar magnetic field will have reversed polarity," said Dr. Edward J. Smith, Ulysses project scientist at JPL. "We expect the profile we obtain five years from now will be dramatically different and give us many new insights into the dynamics of this star at the center of our solar system."
Based on the importance of its investigations and the excellent condition of the spacecraft, the Ulysses mission will continue through a second set of polar passes beginning in September 2000. At the conclusion of its mission in December 2001, the spacecraft will have collected data on solar phenomena at all latitudes during the quietest and most active phases of the 11-year solar cycle.
The Ulysses mission is an international project of the European Space Agency and NASA to explore regions of space above and below the Sun's poles. The Jet Propulsion Laboratory manages the U.S. portion of the mission for NASA's Office of Space Science, Washington, D.C.
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