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Matching meteorites with their parents.

Astronomers report the first direct link between a set of meteorites and a particular location in the main asteroid belt, which lies between Mars and Jupiter.

Michael J. Gaffey, Kevin L. Reed and Michael S. Kelley of the Rensselaer Polytechnic Institute in Troy, N.Y., made their chance discovery after observing the asteroid Apollo (3103) 1982BB as it passed within 30 million kilometers of Earth in July 1991. Obtaining the asteroid's spectra with the NASA Infrared Telescope atop Mauna Kea in Hawaii, the researchers found evidence that the body contained a type of iron-free, magnesium-rich silicate known as enstatite. That mineral also predominates in a group of meteorites called enstatite achondrites. Gaffey's team believes these meteorites represent fragments of the kilometer-size asteroid they studied.

At first glance, that identification wouldn't seem to link meteorites with main-belt asteroids, since (3103) 1982BB does not now reside in the belt. But it may have once, says Gaffey, since this asteroid's orbit intersects the Hungaria region, one of the innermost parts of the asteroid belt.

Researchers had previously suspected that enstatite achondrites came from the Hungaria region, but they discounted the idea because the surfaces of meteorites falling to Earth directly from this locale would have been bombarded by cosmic rays for tens of millions of years. Cosmic-ray studies, however, have shown that enstatite achondrites experienced such bombardment about 10 times longer.

Gaffey's team conjectures that the Apollo asteroid represents a chip off an old rock, a runaway fragment of a larger resident of the Hungaria region. As such, it could have served as a reservoir for the enstatite meteorites, which at some point broke off its surface, accounting for their longer exposure in space. Thus, Hungaria asteroids indeed appear to be the parent bodies of these meteorites, Gaffey concludes. The link may enable researchers to infer the composition and temperature of this part of the solar system during the formation of the planets and asteroids, he notes.
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Title Annotation:Lunar and Planetary Science Conference report
Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:Apr 4, 1992
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