Issue Date: March 3, 2008
Graphite Whiskers Found In Meteorites
Whiskers made of graphite have been discovered in meteorites, lending credence to a long-held idea that they may exist in outer space.
This in turn may help explain why radiation from some astronomical objects appears dimmed. Astronomers have suggested that needle shapes—whether silicon, graphite, or iron—may be present in interstellar dust, absorbing visible light from some supernovas and infrared light from the centers of some galaxies.
Now, for the first time, scientists have examples of graphite whiskers in hand, and "this should result in a better understanding of the basic physical workings of our universe," Marc D. Fries says. Fries, along with astrobiologist Andrew Steele, at the Carnegie Institution of Washington, in Washington, D.C., examined several carbonaceous chondrite-type meteorites, the sort thought to be formed in the early solar system.
Using electron microscopy and Raman spectroscopy on meteorite samples, they found calcium-aluminum inclusions that contained the needlelike graphite structures (Science, DOI: 10.1126/science.1153578).
The needles, which form from the condensation of carbon-rich gases, are little sheets of rolled-up graphite. They also have been formed in labs on Earth and sometimes as nuisance artifacts in the industrial fabrication of smooth surfaces. Out in space, whiskers might have been created during formation of the very early solar system and then spewed out into the interstellar medium.
If such whiskers were the cause of light dimming in space, they would act like little antennas, explains Eli Dwek, astronomer at NASA's Goddard Space Flight Center, who calls the discovery "exciting." Only a small percentage of interstellar material needs to be needle-shaped to cause the effect, he says.
However, Dwek says the length of the needles determines the wavelength of light they can absorb. The whiskers discovered by Fries and Steele are about 1–2 μm long, but to absorb infrared or microwave radiation, the needles would need to be much longer. Whether the whiskers exist in longer form out in space is still a mystery.
The whiskers' dimming effects could also carry implications for the mysterious "dark energy" that has been postulated to explain the acceleration of the expansion of the universe, support for which is partly based on supernova brightness.
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