Computer Simulation Predicts Voyager 2 Spacecraft Will Reach Major Milestone Soon
- From: baalke@xxxxxxxxxxxxx
- Date: Wed, 28 Nov 2007 15:53:27 -0800 (PST)
http://www.newsroom.ucr.edu/cgi-bin/display.cgi?id=1720
Computer Simulation by UCR Physicist Predicts Voyager 2 Spacecraft
Will
Reach Major Milestone in Space in Late 2007 or Early 2008
According to model, spacecraft will cross "termination shock" one more
time, in mid-2008
(November 27, 2007)
RIVERSIDE, Calif. - Using a computer model simulation, Haruichi
Washimi,
a physicist at UC Riverside, has predicted when the interplanetary
spacecraft Voyager 2 will cross the "termination shock," the spherical
shell around the solar system that marks where the solar wind slows
down
to subsonic speed.
According to Washimi's simulations, the spacecraft is set to cross the
termination shock in late 2007-early 2008. To make this forecast,
Washimi and his colleagues used data from Voyager 2 and performed a
global "magneto-hydrodynamic simulation" - a method that allows for
precise and quantitative predictions of geomagnetic disturbances
caused
by solar activities.
Because Voyager 2's crossing of the shock is expected to be an abrupt
and relatively brief event, scientists are working to ensure that the
most is made of the opportunity. With an idea of when the spacecraft
will cross the shock, they are better able to maximize coverage of the
crossing.
Study results appear in the Dec. 1 issue of The Astrophysical Journal.
"Washimi's model has predicted the location of a boundary that is
approximately 90 times farther from the sun than is the Earth, to
within
a few percent," said Gary Zank, the director of the Institute of
Geophysics and Planetary Physics <http://www.igpp.ucr.edu/> and one of
the coauthors of the research paper. "This is truly remarkable given
the
enormous complexity of the physics involved, the temporal and spatial
scales involved, and the variability of the solar wind conditions."
The solar wind - a stream of charged particles ejected by the sun in
all
directions - travels at supersonic speeds when it leaves the sun,
until
it eventually encounters the interstellar medium made up of plasma,
neutral gas and dust.
At the termination shock, located at 7-8.5 billion miles from the sun,
the solar wind is decelerated to less than the speed of sound. The
boundary of the termination shock is not fixed, however, but wobbly,
fluctuating in both time and distance from the sun, depending on solar
activity.
"This is the first time the termination-shock position has been
forecast
in this way," said Washimi, the lead author of the research paper and
a
scientist at the Institute of Geophysics and Planetary Physics. "After
it crosses this boundary, Voyager 2 will be in the outer heliosphere
beyond which lies the interstellar medium and galactic space. Our
simulations also show that the spacecraft will cross the termination
shock again in the middle of 2008. This will happen because of the
back
and forth movement of the termination-shock boundary. This means
Voyager
2 will experience multiple crossings of the termination shock. These
crossings will come to an end after the spacecraft escapes into
galactic
space."
Voyager 2 was launched Aug. 20, 1977. It visited four planets and
their
moons in the course of its journey into space. Its sister spacecraft
Voyager 1, which was launched Sept. 5, 1977, crossed the termination
shock in December 2004 - earlier than Voyager 2 because of a shorter
trajectory. Both spacecraft are currently operational, but power
sources
have degraded and some of the instrumentation no longer works
optimally.
In the future, the spacecraft will encounter their next milestone in
space: the heliopause, which is the boundary where the interstellar
medium brings the solar wind to a halt.
Washimi and Zank <http://www.igpp.ucr.edu/People_Zank.htm> were joined
in the research by UCR's Qiang Hu; Takashi Tanaka of Kyushu
University,
Japan; and Kazuoki Munakata of Shinshu University, Japan. The research
was funded by grants from the National Science Foundation and the
National Aeronautics and Space Administration.
The Institute of Geophysics and Planetary Physics at UCR is a
multi-campus research unit whose mission is to promote basic research
in
the structure, origin, and evolution of the universe including the
solar
system and its planets. Its objectives are to encourage, foster and
support basic research in astrophysics, planetary physics and
geophysics; to foster research and collaboration between the UC
campuses, national laboratories, and across colleges and departments
at
UCR; and to contribute to graduate education in cooperation with other
units in the University of California.
.
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