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Meteorite sample older than sun sheds light on solar system. ARCHAEOLOGY OF THE SKY

Scientists who study the origin of the solar system have found some of the oldest material yet known. It's a compound of carbon and silicon, rarely found in nature, which was formed by stars that burned before our sun was born some 4.6 billion years ago.

This exotic substance has recently been extracted from a sample of the 50-pound stony meteorite that fell near Murray, Kentucky in 1950. It provides a link between what scientists can study in their laboratories today and ancient cosmic events that contributed to our solar system.

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The silicon-carbide content is tiny. It constitutes only a few parts in 100,000 of the silicon content of the meteorite sample. The sample, which itself weighs only 0.46 ounces, was analyzed by teams at the University of Chicago, Washington University in St. Louis, Mo., and the Monsanto Company Research Center.

It took rough physical processing and strong acid treatments to recover the silicon carbide. ``To find the needle in the haystack, we simply burned down the haystack,'' observes University of Chicago chemist Edward Anders in describing this drastic process.

The ability to isolate and identify this minuscule amount of material in a meteorite - a feat impossible even 10 years ago - ``is a breathtaking illustration of what microanalysis can now accomplish,'' says the editor of the journal Nature, whose year-end edition reports the discovery.

More than that, the material can help scientists better understand what went into the solar nebula - the cloud of dust and gas which condensed into our sun and its planets.

We know silicon carbide in its man-made form as carborundum, a widely used industrial abrasive. But it is unusual to find it naturally in the solar system. Silicon combines more readily with oxygen than with carbon. Material that formed the solar nebula originated mainly in oxygen rich stars. Thus the natural occurrence of the silicon-carbon compound rather than a silicon-oxygen compound suggests the material originated in a carbon rich star - perhaps a red giant in a late stage of its evolution.

The finding encourages the expectation that scientists will be able to get a new perspective on the origin of the solar nebula.

Looking ahead, Nature editor John Maddox notes that ``the wealth of detail likely to emerge from further research by Anders and his colleagues promises to specify the nature of the stars contributing to the nebula.''

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Earlier this year, Mr. Anders's team announced isolation of diamonds - another pre-solar material - in a sample of the Murchison meteorite that fell in Australia in 1969.

Discovery of these hard-to-destroy meteoritic materials helps prove that their parent bodies do contain the dust of pre-solar stars.

``It is fortunate that these exotic [materials] come to us undiluted ... and in a chemically resistant form that permits them to survive destruction processes in interstellar space, meteorite parent bodies, and ... the laboratory,'' say the discoverers in their Nature report.

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