From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Nov 05 2003 - 14:05:14 PST
----- Original Message -----
From: NASA Jet Propulsion Laboratory
Sent: Wednesday, November 05, 2003 5:00 PM
To: ljk4_at_msn.com
Subject: Voyager Spacecraft Approaches Solar System's Final Frontier
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Carolina Martinez (818) 354-9382
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Nancy Neal (301) 286-0039
Goddard Space Flight Center, Greenbelt, Md.
NEWS RELEASE: 2003-145 November 5, 2003
Voyager Spacecraft Approaches Solar System's Final Frontier
NASA's venerable Voyager 1 spacecraft, built and operated by NASA's
Jet Propulsion Laboratory, Pasadena, Calif., is about to make history
again. It is the first spacecraft to enter the solar system's final
frontier, a vast expanse where wind from the Sun blows hot against
thin gas between the stars: interstellar space.
However, before it reaches this region, Voyager 1 must pass through
the termination shock, a violent zone that is the source of beams of
high-energy particles. Voyager's journey through this turbulent zone
will give scientists the first direct measurements of our solar
system's unexplored final frontier, the heliosheath. Scientists are
debating whether this passage has already begun. Two papers about this
research are being published in Nature today.
The first paper, by Dr. Stamatios Krimigis of the Johns Hopkins
University Applied Physics Laboratory, Laurel, Md., and his team,
supports the claim Voyager 1 passed beyond the termination shock. The
second paper, by Dr. Frank McDonald of the University of Maryland,
College Park, and his team, disputes the claim. A third paper,
published October 30 in Geophysical Research Letters by Dr. Leonard
Burlaga of Goddard Space Flight Center, Greenbelt, Md., and
collaborators, states Voyager 1 did not pass beyond the termination
shock.
"Voyager 1 has seen striking signs of the region deep in space where a
giant shock wave forms, as the wind from the Sun abruptly slows and
presses outward against the interstellar wind. The observations
surprised and puzzled us, so there is much to be discovered as it
begins exploring this new region at the outer edge of the solar
system," said Dr. Edward Stone, Voyager project scientist at the
California Institute of Technology in Pasadena.
Launched on September 5, 1977, Voyager 1 explored the giant planets
Jupiter and Saturn before being tossed out toward deep space by
Saturn's gravity. It is approaching, and may have temporarily entered,
the region beyond termination shock. At more than 13 billion
kilometers (approximately eight billion miles) from the Sun, Voyager 1
is the most distant object from Earth built by humanity.
The termination shock is where the solar wind, a thin stream of
electrically charged gas blown constantly from the Sun, is slowed by
pressure from gas between the stars. At the termination shock, the
solar wind slows abruptly from its average speed of about 700,000 to
1,500,000 miles per hour.
Estimating the location of the termination shock is hard, because we
don't know the precise conditions in interstellar space. We do know
speed and pressure of the solar wind changes, which cause the
termination shock to expand, contract and ripple.
>From about August 1, 2002 to February 5, 2003, scientists noticed
unusual readings from the two energetic particle instruments on
Voyager 1, indicating it had entered a region of the solar system
unlike any previously encountered. This led some to claim Voyager 1
may have entered a transitory feature of the termination shock.
The controversy would be resolved if Voyager could measure the speed
of the solar wind, because the solar wind slows abruptly at the
termination shock. However, the instrument that measured solar wind
speed no longer functions on the spacecraft. Scientists must use data
from instruments that are still working to infer if Voyager pierced
the termination shock.
"We have used an indirect technique to show the solar wind slowed down
from about 700,000 miles per hour to much less than 100,000 mph. We
used this same technique when the instrument measuring the solar wind
speed was still working. The agreement between the two measurements
was better than 20 percent in most cases," Krimigis said.
"The analysis of the Voyager 1 magnetic field observations in late
2002 indicate that it did not enter a new region of the distant
heliosphere by having crossed the termination shock. Rather, the
magnetic field data had the characteristics to be expected based upon
many years of previous observations, although the intensity of
energetic particles observed is unusually high," Burlaga said.
Voyagers 1 and 2 were built by JPL, which continues to operate both
spacecraft 26 years after their launch. The spacecraft are controlled
and their data returned through NASA's Deep Space Network, a global
spacecraft tracking system also operated by JPL. The Voyager Project
Manager is Ed Massey of JPL. For their original missions to Jupiter
and Saturn, the Voyagers were destined to explore regions of space
where solar panels would not be feasible, so each was equipped with
three radioisotope thermoelectric generators to produce electrical
power for the spacecraft systems and instruments. Still operating in
remote, cold and dark conditions 26 years later, the Voyagers owe
their longevity to these Department of Energy-provided generators,
which produce electricity from the heat generated by the natural decay
of plutonium dioxide.
More information about the Voyagers is available at:
http://voyager.jpl.nasa.gov/ .
For images and animation on the Internet, visit:
http://www.gsfc.nasa.gov/topstory/2003/1105voyager.html .
-end-
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