The Ulysses spacecraft, on a mission to explore the Sun at extreme latitudes, today begins its investigation of the Sun's south polar region. This will be the second time Ulysses has passed under the Sun, but this time the glowing orb will look and act very differently because the Sun has reached solar maximum, a time of heightened activity.
Ulysses was able to assess the Sun during the relatively quiet solar minimum between 1994 and 1996. Now it will fill in the gaps with observations during the solar maximum, thus completing observations during a full sunspot cycle of 11 years.
"Ulysses has been making continuous observations of the Sun and heliosphere for the last 10 years," said the U.S. project scientist for Ulysses, Dr. Edward Smith of NASA's Jet Propulsion Laboratory, Pasadena, California. "The scientists involved are still as enthusiastic as ever and are looking forward to discovering lots of new things as the Sun acts up."
Scientists are interested in learning about sunspots, solar flares and coronal mass ejections, chunks of the Sun's outer atmosphere that blow off into space and can strike the Earth, causing aurorae and interrupting satellite communications.
The scientific investigations on Ulysses are studying the Sun's corona, its gaseous outer atmosphere, which extends far beyond the orbit of Earth. This gas moves outward through the solar system at high speed, and therefore is called the solar wind. In addition to affecting Earth and other planets, this wind pushes the gas and dust that occupies the space between the stars out of the solar system and forms a " bubble" in the interstellar medium called the heliosphere. In spite of the Sun's effort to keep out interstellar matter, some of the gas and dust penetrates the bubble and is found throughout the heliosphere. A major goal of Ulysses is to study incoming cosmic rays -- nuclei of atoms travelling at nearly the speed of light -- and how they interact with the solar wind.
During its first passage over the Sun's poles at solar minimum, Ulysses showed that there are two kinds of solar wind -- slow wind near the equator and very fast wind near the poles. Ulysses has found that although the Sun's magnetic field is strongest near the poles, as the solar wind pushes it outward, the magnetic field eventually has the same strength over the equator as over the poles. The spacecraft will measure the magnetic field around the Sun and the ions emanating from it. It will try to find out how changes in the strength and direction of the magnetic field affect both the solar wind, coming from the Sun, and the cosmic rays, coming toward the Sun.
During the previous solar polar passes, scientists had expected to find that the cosmic rays would be funneled toward the poles by the Sun's magnetic field. But this wasn't what they found, at least not during solar minimum. Will this be the case during solar maximum? The Ulysses team hopes to find out.
Ulysses is the only spacecraft to reach such high solar latitudes. Most spacecraft -- like the planets -- move around the Sun in slightly tilted planes, compared to the Sun's equator. Ulysses has gone well above the solar equator, as far as 80 degrees north and south solar latitudes -- equivalent on Earth to traveling from the northern tip of Greenland to Antarctica in the south.
Ulysses, launched in 1990, is a joint venture of NASA and the European Space Agency. JPL manages Ulysses for NASA's Office of Space Science, Washington, D.C. More information on the Ulysses mission is available at the JPL Ulysses website: http://ulysses.jpl.nasa.gov and the ESA Ulysses website, http://helio.estec.esa.nl/ulysses/ .
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