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Lawrence Livermore National Laboratory News Release

Contact: Anne Stark                      FOR IMMEDIATE RELEASE
Phone: (925) 422-9799                    June 5, 2003
E-mail:stark8{at}llnl.gov                   NR-03-06-02

Astrophysicists Simulate Comet X-Ray Emissions In Laboratory

LIVERMORE, Calif. - Physicists from the Lawrence Livermore National
Laboratory have produced X-ray emissions in a laboratory setting by
recreating the conditions that exist when solar winds collide with
gases surrounding comets. 

Using the electron beam ion trap facility located at Livermore
Laboratory, physicists Peter Beiersdorfer, Hui Chen and Mark May
created charge exchange between heavy ions to produce X-ray
emissions, similar to what happens when solar wind and gases collide
in a comet. 

In collaboration with researchers from NASA Goddard Space Flight
Center, Columbia University Department of Physics and the University
of Missouri-Rolla Department of Physics, the team will present
"Laboratory Simulation of Charge Exchange-Produced X-ray Emission
From Comets" in the June 6 edition of Science. 

The researchers studied charge exchange-induced cometary X-ray
emissions by installing the spare X-ray microcalorimeter
spectrometer (XRS) from the ASTRO-E satellite mission onto
Livermore's existing electron beam ion trap. The XRS was designed to
view distant objects such as supernova remnants with a higher
spectral resolution than is available at the Chandra X-ray
Observatory. 

Beiersdorfer said that cometary X-rays can serve as a diagnostic for
solar activity and hence "space weather" by measuring the quantity
and composition of the heavy ion flux in solar wind. In addition,
recent work has shown that emissions can be a potential tool to gauge
the speed of the solar wind. 

"Because comets enter the solar system from different directions in
and out of the ecliptic, they probe regions that are not covered by
spacecraft," he said. 

Cometary X-ray emissions form when a continuous stream of charged
heavy ions in the solar wind collide with the gases surrounding the
nucleus of a comet.. The collision is believed to neutralize the
solar wind ions and induce them to give off X-rays characteristic of
the ions and gases involved in the collision. 

Actual X-ray emissions have been observed at the Chandra X-ray
Observatory. In the Livermore experiments, the Goddard
microcalorimeter recorded X-ray data that explained the emission seen
from comets in the solar system. 

"Next to the Sun, the process we demonstrated here at Livermore makes
comets the strongest X-ray emitters in the solar system,"
Beiersdorfer said. 

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Founded in 1952, Lawrence Livermore National Laboratory is a national
security laboratory, with a mission to ensure national security and
apply science and technology to the important issues of our time.
Lawrence Livermore National Laboratory is managed by the University
of California for the U.S. Department of Energy's National Nuclear
Security Administration. 

Laboratory news releases and photos are also available electronically
on the World Wide Web of the Internet at URL http://www.llnl.gov/PAO
and on UC Newswire.

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