U.Iowa researchers make first measurements of the solar wind termination shock (Forwarded)

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University of Iowa
Iowa City, Iowa

MEDIA CONTACTS:

Don Gurnett, principal investigator
319-335-1697

Bill Kurth, co-principal investigator
319-335-1926

Gary Galluzzo, University News Services
319-384-0009

July 3, 2008

UI researchers make first measurements of the solar wind termination shock

Two University of Iowa space physicists report that the Voyager 2
spacecraft, which has been traveling outward from the sun for 31 years, has
made the first direct observations of the solar wind termination shock,
according to a paper published in the July 3 issue of the journal Nature.

At the termination shock the solar wind, which continuously expands outward
from the sun at over a million miles per hour, is abruptly slowed to a
subsonic speed by the interstellar gas. Don Gurnett, professor of physics in
the College of Liberal Arts and Sciences and principal investigator for the
plasma wave instrument on Voyager 2, and Bill Kurth, UI research scientist
and Voyager co-investigator, said that the shock crossing was marked by an
intense burst of plasma wave turbulence detected by the UI instrument, as
well as by various effects detected by other instruments on the spacecraft.

At the time of the shock crossing, August 31, 2007, Voyager 2 was at a
distance of 83.7 astronomical units (AU), roughly twice the distance between
the sun and Pluto. At this great distance, it took 11.2 hours for the radio
signal from the spacecraft to reach Earth.

Shock waves in the thin, ionized gas -- called plasma -- that exists in
space are similar in some respects to the shock waves produced by an
airplane in supersonic flight. Shock waves in space are believed to play an
important role in the acceleration of cosmic rays, which are very energetic
atomic particles that continually bombard Earth. The most energetic cosmic
rays, which are potentially hazardous to astronauts, are believed to be
produced in intense shock waves caused by supernova explosions -- immense
stellar explosions that occur in massive stars toward the end of their
lives.

The termination shock is believed to be responsible for the origin of less
energetic cosmic rays called "anomalous cosmic rays." The recent
observations at the termination shock are expected to help physicists
understand how cosmic rays are produced by the turbulent fields that exist
in such shocks. Gurnett said, "There is no way for us to make direct measure
of a supernova shock, so the Voyager 2 measurements at the termination shock
provide us the best opportunity in the foreseeable future to understand how
cosmic rays are produced by supernova cosmic shocks."

Kurth noted that while some aspects of the termination shock matched
scientists' expectations, a number of the observations made by Voyager were
surprising and will cause a number of theories to be revised.

Gurnett noted that Voyager 2, launched in 1977, is moving at a speed of
38,000 miles an hour. Even at this considerable speed, the spacecraft will
still take 30,000 years to reach a distance equal to that of the nearest
star.

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

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

IMAGE CAPTION:
[http://news-releases.uiowa.edu/2008/...t-Voyager2.jpg
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The location of the Voyager 2 spacecraft and its Voyager 1 sister craft
relative to the Sun, the termination shock and other solar system structures
can be seen in this artist's image provided by NASA.