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New radiation belt spotted around Earth.

A joint U.S.-German satellite launched last year has identified a belt of radiation around Earth that holds an unusual collection of matter from outside the solar system. The discovery of these exotic ions trapped in orbit provides an opportunity to study the environment beyond our solar system without having to leave Earth's own backyard, say space scientists who announced the findings last week in Baltimore at a meeting of the American Geophysical Union.

"What's exciting about this is that it's a sample of matter from a place that we'd like to be able to study. We'll be able to do it because it's right here," says Jay R. Cummings, a member of the satellite team and a space physicist at the California Institute of Technology in Pasadena.

The new information comes from measurements made by the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), the first of a trio of small, quickly built satellites that NASA hopes will bypass the normally plodding process that can take a decade from planning to launch. SAMPEX circles the Earth at an altitude of 600 kilometers.

The radiation belt identified by SAMPEX joins two others that were discovered in 1958 by physicist James A. Van Allen of the University of Iowa in Iowa City. All three belts hold electrically charged particles that have become trapped by Earth's magnetic field. The outer Van Allen belt contains mostly energetic electrons, while the inner Van Allen holds mostly fast-moving protons. The newly discovered belt resides within the inner Van Allen belt and stores energetic ions of oxygen, nitrogen, and neon, says SAMPEX scientist Richard A. Mewaldt of Caltech.

The scientists believe this collection of ions is a trapped form of so-called anomalous cosmic rays. Unusual because of their composition and charge, such rays are born in a complex process that starts outside the solar system in the interstellar medium, which contains debris from supernovas, remnants of the Big Bang, and other matter.

As our solar system moves through the interstellar medium, the flow of protons emanating from the sun pushes aside any charged particles. But this solar wind does not affect neutral elements, which can slip into the solar system. As the elements drift toward the sun, solar radiation bombards them, stripping one electron from each and forming ions. These ions feel the push of the solar wind and are carried to the edge of the solar system. There they hit a magnetic shock wave that energizes them and forms the anomalous cosmic rays, some of which head toward Earth.

In 1977, J. Bernard Blake and Lynn T. Friesen of The Aerospace Corporation in El Segundo, Calif., proposed that such anomalous cosmic rays could become trapped in Earth's magnetic field if they passed close enough to hit atmospheric particles and lose all of their electrons. Once stripped, the ions would fly between magnetic poles, spiraling around the magnetic field lines.

Data collected in the late 1980s by Soviet COSMOS satellites first detected signs of such cosmic rays trapped in a radiation belt around Earth. But those measurements could not identify the precise location of the belt or much of its contents, says Cummings.

To its discoverers, the !and of trapped cosmic rays represents a third radiation belt. But because the original Van Allen belts contain different types of particles, Van Allen himself thinks the trapped cosmic rays are one group within that inner radiation belt, he told SCIENCE NEWS. Others argue that the trapped ions constitute a new belt because they come from a different location. Many of the other belt constituents hail from Earth itself.

Beyond that nominal issue, space scientists say the discovery of trapped cosmic rays in a belt around Earth offers a unique chance to obtain samples of matter from beyond the confines of our immediate stellar environment. That's important because almost everything else within the solar system is related, having condensed from the same cloud of gas and dust 4.65 billion years ago. Says Blake, who predicted the existence of a new radiation belt, "One would like to get samples of material from elsewhere. Well, cosmic rays are messengers from a distance."
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Author:Monastersky, Richard
Publication:Science News
Date:Jun 5, 1993
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