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U.Iowa's Gurnett Says Voyager 1 Reaches Milestone On Journey ToInterstellar Space (Forwarded)



 
 
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Old May 24th 05, 04:58 PM
Andrew Yee
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Default U.Iowa's Gurnett Says Voyager 1 Reaches Milestone On Journey ToInterstellar Space (Forwarded)

News Services
University of Iowa
300 Plaza Centre One, Suite 301
Iowa City, Iowa 52242-2500

CONTACTS:

Media:
Gary Galluzzo, 319-384-0009,

Program:
Don Gurnett, Project Principal Investigator
319-400-3156,


News Release: May 24, 2005

UI's Gurnett Says Voyager 1 Reaches Milestone On Journey To Interstellar
Space

University of Iowa space physicist Don Gurnett says that NASA's Voyager 1
spacecraft -- the most distant manmade object at some 94 astronomical
units (AU) or more than 8.7 billion miles from the sun -- has crossed a
boundary called the "termination shock," one of the last milestones it
will encounter before leaving the solar system and entering interstellar
space.

Gurnett, professor of physics in the UI College of Liberal Arts and
Sciences and principal investigator for the plasma wave instrument on
Voyager 1, will present his findings at a May 24 news conference during
the spring 2005 meeting of the American Geophysical Union in New Orleans.
Evidence for the crossing, which occurred December 16, 2004, included
steadiness in the strength of energetic particle beams, a near reversal of
the direction of these beams and a jump in the magnetic field strength. An
electron beam generated by the termination shock created the electron
plasma oscillations observed by Gurnett's team.

"We saw a burst of plasma oscillations before we went through the
termination shock," he says. "There's a consensus among Voyager scientists
that we crossed the termination shock at 94 AU. This is something that
Bill Kurth, (UI research scientist and Voyager co-investigator) and I
predicted several years ago in a published paper."

Kurth compares the termination shock to what happens when water is allowed
to run from a kitchen faucet onto the center of a dinner plate. The water
-- representing the solar wind, a stream of electrically charged particles
flowing outward from the sun -- strikes the center of the plate and
smoothly flows outward in all directions. Somewhere near the edge of the
plate, the smooth stream becomes rippled as it runs into slower moving
water. This rippled band of turbulence represents the termination shock
and the region where it occurs, the heliosheath. Similarly, the solar wind
slows from supersonic to subsonic speed as it approaches the gas generated
by stars beyond our sun.

"The solar wind creates a bubble (the heliosphere) around the sun, and
near the edges of the bubble is a place where the solar wind piles up as
it encounters the interstellar wind," says Ed Stone, Voyager project chief
scientist and professor of physics at the California Institute of
Technology. "We think the sun is currently in a phase where the
heliosphere is shrinking. If so, Voyager would continue to be in this
thicker and hotter region until it reaches the heliopause, the outer edge
of the bubble. This is a wonderful opportunity to reach interstellar
space, and we hope we can keep the spacecraft operating through the year
2020."

Nobody knows precisely when Voyager will reach the heliopause, but Gurnett
notes that estimates of the distance of the heliopause from the sun have
varied widely, ranging from one scientist's 1956 estimate of 5 AU to
Gurnett's estimate of 126-168 AU made in 1993. Today, he says that the
termination shock just encountered is probably about three-quarters of the
way there, placing interstellar space about 25 to 35 AU beyond Voyager's
current position. With the spacecraft moving at about 3.5 AU per year,
Voyager 1 may reach the heliopause in another 10 years or so -- a long
journey for a mission that began with a Sept. 5, 1977 launch and
successful fly-bys of both Jupiter and Saturn. A sister spacecraft,
Voyager 2 was launched Aug. 20, 1977, on a flight path that took it to
encounters with Jupiter, Saturn, Uranus and Neptune. At present Voyager 2
is about 76 AU from the sun and traveling at about 3.3 AU per year.

The sounds of Voyager's encounter with the termination shock and other
sounds of space can be heard by visiting Gurnett's Web site at:
http://www-pw.physics.uiowa.edu/space-audio/

NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif., a division of
Caltech, manages the Voyager mission for NASA's Office of Space Science,
Washington, D.C.

 




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