MIT solves puzzle of meteorite-asteroid link

New analysis makes it possible to 'know our enemy'

David Chandler, MIT News Office

August 13, 2008

For the last few years, astronomers have faced a puzzle: The vast majority of asteroids that come near the Earth are of a type that matches only a tiny fraction of the meteorites that most frequently hit our planet.

Since meteorites are mostly pieces of asteroids, this discrepancy was hard to explain, but a team from MIT and other institutions has now found what it believes is the answer to the puzzle. The smaller rocks that most often fall to Earth, it seems, come straight in from the main asteroid belt out between Mars and Jupiter, rather than from the near-Earth asteroid (NEA) population.

The puzzle gradually emerged from a long-term study of the properties of asteroids carried out by MIT professor of planetary science Richard Binzel and his students, along with postdoctoral researcher P. Vernazza, who is now with the European Space Agency, and A.T. Tokunaga, director of the University of Hawaii's Institute of Astronomy.

By studying the spectral signatures of near-Earth asteroids, they were able to compare them with spectra obtained on Earth from the thousands of meteorites that have been recovered from falls. But the more they looked, the more they found that most NEAs -- about two-thirds of them -- match a specific type of meteorites called LL chondrites, which only represent about 8 percent of meteorites. How could that be?

"Why do we see a difference between the objects hitting the ground and the big objects whizzing by?" Binzel asks. "It's been a headscratcher." As the effect became gradually more and more noticeable as more asteroids were analyzed, "we finally had a big enough data set that the statistics demanded an answer. It could no longer be just a coincidence."

Full article here:

The puzzle gradually emerged from a long-term study of the properties of asteroids carried out by MIT professor of planetary science Richard Binzel and his students, along with postdoctoral researcher P. Vernazza, who is now with the European Space Agency, and A.T. Tokunaga, director of the University of Hawaii’s Institute of Astronomy.

By studying the spectral signatures of near-Earth asteroids, they were able to compare them with spectra obtained on Earth from the thousands of meteorites that have been recovered from falls. But the more they looked, the more they found that most NEAs — about two-thirds of them — match a specific type of meteorites called LL chondrites, which only represent about 8 percent of meteorites. How could that be?

“Why do we see a difference between the objects hitting the ground and the big objects whizzing by?” Binzel asks. “It’s been a headscratcher.” As the effect became gradually more and more noticeable as more asteroids were analyzed, “we finally had a big enough data set that the statistics demanded an answer. It could no longer be just a coincidence.”

Full article here:

http://web.mit.edu/newsoffice/2008/meteorites-0813.html