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

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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.

In message , A. Yee
writes

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.

This is a wonderful opportunity to reach interstellar space, and we
hope we can keep the spacecraft operating through the year 2020."

Interesting! But has any decision been taken on shutting down the
Voyagers _this year_ ?
http://www.nasawatch.com/archives/2005/03/nasa_to_shut_do.html
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