BRONX, N.Y.—March 26, 2009: Mysterious lights in the sky just became a little less mysterious, partly through the work of Jon Friedrich, Ph.D., an assistant professor of chemistry at Fordham University. By analyzing the bulk chemistry of meteorite fragments recovered in Sudan, Friedrich and his colleagues have given astronomers the ability to tell the chemical composition of certain asteroids from spectroscopic analysis. Their work is described in the cover story of the March 26 issue of Nature.
“It is amazing to be able to finally positively link an asteroid to a certain type of meteorite,” said Friedrich. “When we look at asteroids in space were only looking at the outside, and the asteroid’s surface has changed from being in the environment of space. For the first time we can actually say, 100 percent without hand waving, how the surface characteristics don’t match the interior. That knowledge gives us a map as to how the exteriors of asteroids change. We can have a better understanding of the population of objects in space and their distribution in the solar system, and what that means for diversity of objects in the solar system.”
Though scientists have been able to catalog thousands of asteroids through spectroscopic analysis, and tens of thousands of meteorites (asteroid particles that survive the plunge through Earth’s atmosphere), they have never been able to unequivocally connect a meteorite with its parent asteroid.
On October 7, 2008, asteroid 2008 TC3, discovered by the automated Catalina Sky Survey Telescope at Mt. Lemmon, Arizona, crashed into northern Sudan, becoming the first asteroid to ever be spectrally classified before striking a planet. Scientists didn’t expect to find pieces of the asteroid because it exploded at the unusually high altitude of 37 kilometers (about 23 miles), but when Peter Jenniskens, Ph.D., of the SETI Institute and lead author on the paper, led an expedition along the approach trajectory in northern Sudan, they recovered 47 meteorites with a total mass of 3.95 kilograms (8.7 pounds). The meteorite search was joined by faculty and students at the University of Khartoum.
Analysis of the fragments, collectively named Almahata Sitta, revealed a rare, carbon-rich type of meteorite called an ureilite. Ureilites are believed to come from a large organic–rich, primitive asteroid that had melted sometime in its past. The spectroscopic signature of the meteorite and parent asteroid is most similar to F class asteroids, which can now be linked to dark carbon-rich anomalous ureilites. Few ureilites exist in meteorite collections and Almahata Sitta’s unusually fine-grained and porous texture makes it extremely fragile—which is why Almahata Sitta shattered high in Earth’s atmosphere.
Almahata Sitta’s fragile texture suggests that it came from the surface of the original asteroid. This finding makes it especially valuable to planetologists studying the geological history of primitive bodies, planning spacecraft missions to asteroids and working on ways to mitigate the threat posed to Earth by asteroids that cross its orbit.
Jon M. Friedrich received his Ph.D. in analytical chemistry from Purdue University. He was appointed to the Fordham faculty in 2006, and is a research associate in the Department of Earth and Planetary Sciences at the American Museum of Natural History. His research interests include analysis of chondrites for the investigation of planetary evolutionary processes and chemical processes, chronology and diversity in the early solar system.