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NEWS
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March 31, 1998
AGU RELEASE NO. 98-08 For Immediate Release |
Contact: Harvey Leifert
(202) 777-7507 hleifert@agu.org |
WASHINGTON, D.C. - Two astrophysicists have proposed a method for determining the location of the heliopause, the farthest extent of the Sun's influence, through the study of reflected extreme-ultraviolet (EUV) radiation. They report their theory in the forthcoming April 15 issue of Geophysical Research Letters, published by the American Geophysical Union.
The researchers, Mike Gruntman of the University of Southern California in Los Angeles and Hans J. Fahr of the Institute for Astrophysics and Extraterrestrial Research in Bonn, Germany, anticipate that the heliopause will be found to be at least 125 times further from the Sun than is the Earth. They note that the Voyager I space probe is currently heading toward the heliopause and should penetrate it in several years, providing the first direct measurements of its distance.
The region between the heliopause and the Sun is called the heliosphere, where solar radiation is a stronger force than that of the interstellar winds emanating from other stars. The heliopause may be thought of as the outer boundary of the solar system, but the heliosphere is not in fact spherical. It bulges on the side facing away from the center of our galaxy, where there are relatively fewer stars providing counterforce to the Sun's radiation.
Therefore, say Gruntman and Fahr, in order to map the heliopause accurately, many more observations are needed than the one-point data Voyager I will provide, and these observations will have to be made from the vicinity of the Earth. They propose measuring reflected EUV radiation, bounced off the heliopause, a technique not previously suggested. They note that currently available instruments are insufficiently sensitive to measure the faint radiation, but add that it is not impossible to improve them by the three orders of magnitude they feel would be required.
Study of the heliopause will help astrophysicists better understand the nature of the Local Interstellar Medium (LISM), the environment beyond the heliosphere consisting of interstellar plasmas, interstellar gas, magnetic fields, and cosmic rays.
Editors: An advance copy of the four page Gruntman and Fahr paper, "Access to the heliospheric boundary: EUV-echoes from the heliopause," is available on request.