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Nanodiamond Stardust Findings May Cloud Picture of Solar System Origins

Although rare on earth, diamonds are commonplace in outer space--or at least tiny ones are. Dubbed "nanodiamonds," the carbon specks are in fact the most prevalent variety of stardust . Conventional wisdom holds that the ancient material formed before the birth of our solar system. Investigators have thus used these relics to examine the origins of our sun and planets. But new work, published in the current issue of the journal Nature, warns that stardust may not be as old as has been assumed.

Meteorites from our solar system¿s asteroid belt contain large quantities of nanodiamonds. Theoretically, then, comet remnants should contain even greater amounts of these ancient particles, because comets form far away from the sun, where more presolar material--and thus nanodiamonds--should survive. To test this theory, Z. R. Dal of Georgia Institute of Technology and colleagues compared the nanodiamond composition of two meteorites with that of comet remnants. The researchers found few, if any, nanodiamonds in the comet fragments. "We presumed that if we studied (micro) meteorites (also known as interplanetary dust particles from comets) from further out in our solar system, we would find more nanodiamonds," remarks team member John Bradley of Lawrence Livermore National Laboratory. "But we¿re just not seeing them."

The scientists offer a few explanations for their findings. The first is that the stardust, instead of being a relic of pre-solar system days, formed within the early solar system. "Our findings are consistent with recent research that has detected nanodiamonds within the accretion discs of other young stars that are similar to our early solar system," Bradley reports. Alternatively, perhaps nanodiamonds really did develop prior to the birth of our sun, but their abundance decreases as distance from the sun increases instead of the other way around. If so, scientists¿ understanding of how material circulates in the early solar system is fundamentally flawed. Future work will help determine whether nanodiamonds are an astronomer¿s best friend, or a false hope.

"The Secrets of Stardust," by J. Mayo Greenberg (Scientific American, December 2000), is available for purchase from the Scientific American Archive.
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