UpDate - Vol. 15, No. 23, Page 11
March 7, 1996
Bartol researchers working with 'Voyager' explorer

     Scientists from the Bartol Research Institute at the University
are exploring the perimeters of our solar system via the spacecraft
Voyager and supercomputers, figuratively speaking.
     Gary P. Zank, Bartol associate professor, is among the scientists
using the data gathered by Voyager to model the solar wind and to
predict what may occur as it reaches the outer limits of the solar
system and interacts with interstellar space.
     An article focusing on his current research has appeared in the
October-December issue of Gather/Scatter magazine, published by the
San Diego Supercomputer Center, a national laboratory for
computational science and engineering.
     The article, "The Global Structure of Our Solar System" is co-
authored by Bartol scientist Henry L. Pauls and Norman F. Ness, Bartol
president.
     Ness is the principal investigator on the Voyager interstellar
mission, has been principal investigator in more than 20 Explorer,
Mariner, Pioneer, Helio and Voyager spacecraft projects since 1961 and
is an acknowledged expert on the measurement of magnetic fields in
space.
     According to Zank, with spacecrafts Voyager and Pioneer 10,
extending their mission beyond Jupiter to the outermost reaches of the
heliosphere, there is an unprecedented opportunity to learn about the
region where the solar system meets interstellar space. However, as
Voyager's odyssey through space continues, there also is a need to
conserve its resources and energy, making it even more imperative to
try to pinpoint where and when interesting phenomena may occur that
can be observed by the spacecraft.
     Zank's research in this area concerns the solar wind (a tenuous
ionized gas that flows from the sun at supersonic speeds), and how it
will interact with the interstellar medium or galactic wind beyond the
limits of heliosphere.
     Unlike the solar wind, the interstellar medium wind, which may be
sub- or supersonic, is only partially ionized, with 50 percent or more
consisting of neutral hydrogen.
     In essence, this means, according to computer models, that the
solar wind encounters a dense hydrogen wall at the boundary of the
heliosphere (in the vicinity of the so-called helipause), a finding
corroborated by data from the Hubble Space Telescope.
     As Zank writes in the article, "Researchers expect the region
where the solar wind and the galactic wind interact to be a region of
abrupt change, where large shock waves separate the two flows."
     Another factor that is considered in the three-dimensional models
of the interaction of the solar wind with interstellar medium is that
the solar wind is faster at the poles of the sun during some solar
epochs as opposed to the wind in the solar ecliptic plane, as
discovered by the Ulysses spacecraft.
     According to the article, the modeling of these phenomena makes
tremendous demands on time and the data capabilities of even
supercomputers. Because of this, not all the factors have been
included, such as magnetic fields and cosmic rays, which will further
advance research in these areas.
     Zank, who received a prestigious National Young Investigator
Award from the National Science Foundation in 1994, joined the Bartol
faculty at the University in 1989.
                                                   -Sue Swyers Moncure