MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contact: Martha J. Heil (818) 354-0850
FOR IMMEDIATE RELEASE
September 6, 2000
ULYSSES STUDIES THE SUN'S POLAR CAP AT SUNSPOT MAXIMUM
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
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,