[meteorite-list] Composition of Apophis Matches LL Chondrite Meteorites

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 12 Oct 2007 10:24:32 -0700 (PDT)
Message-ID: <200710121724.KAA24748_at_zagami.jpl.nasa.gov>

MIT: Asteroid is "practice case" for potential hazards

For Immediate Release FRIDAY, OCT. 12, 2007

Contact:
Elizabeth A. Thomson, MIT News Office
Phone: 1-617-258-5402 Email: thomson at mit.edu

CAMBRIDGE, Mass.--In research that could aid decisions about future
asteroids on a collision course with Earth, MIT researchers have for
the first time determined the composition of a near-Earth asteroid
that has a very slight possibility of someday hitting our planet.

That information could be useful in planning any future space mission to
explore the asteroid, called Apophis. And if the time ever were to
come when this object or another turned out to be on its way toward an
impact on Earth, knowing what it's made of could be one important factor
in deciding what to do about it.

"Basic characterization is the first line of defense," says Richard P.
Binzel, Professor of Planetary Sciences in the Department of Earth,
Atmospheric, and Planetary Sciences (EAPS). "We've got to know the enemy."

Binzel presented the new findings this week at the annual meeting of the
Division for Planetary Sciences of the American Astronomical Society.

Studying the composition of Apophis has been a useful "practice case,"
Binzel says, because "you never know when the real one will come along"
that is on a collision with the Earth. For determining the composition
of a threatening asteroid, Binzel says, "We don't know when the real
test will come, but we're ready."

On April 13, 2029, Apophis will come relatively close to Earth (it will
miss us by about 22,000 miles). But when it comes by again in 2036,
there is a very small possibility - about one chance in 45,000 - that
it could be on a collision course.

So Binzel, working with EAPS graduate students Cristina Thomas and Francesca
DeMeo and others, has been using telescopes on Earth to find
out as much as possible about the nature of Apophis and other asteroids.
Short of putting together a space mission that would take years and cost
hundreds of millions of dollars, such observations are the best way to
find out as much as possible about any space rock that might someday be
coming our way, Binzel says.

Using the MIT Magellan telescope in Chile and NASA's Infrared Telescope
Facility in Hawaii, they have now been able to figure out exactly what
Apophis is made of. "The composition, I think, is really nailed," he says.

The key to understanding the mineral makeup of an asteroid is to compare it
with samples of asteroidal material that have been delivered, free of
charge, to the Earth, in the form of the many thousands of meteorites
that have been collected over the years.

Spectral analysis - measuring how the meteorites reflect light of different
wavelengths - can be used to determine their exact mineral constituents.
Similarly, a spectral analysis of the light reflected from a distant
asteroid shows the same telltale lines that reveal its composition. By
comparing the two kinds of spectra, an asteroid that is just a faraway
pinprick of light can be correlated with a piece of a space rock in the
laboratory.

Binzel and his students were able to use both visible-light and infrared
spectroscopy to show that Apophis is "a good match" for a rare type of
meteorite, known as a type LL chondrite. These represent just 7 percent of
the known meteorite falls on Earth, and are rich in the minerals pyroxene
and olivine, which are also common on Earth.

"The beauty of having found a meteorite match for Apophis is that because we
have laboratory measurements for the density and strength of these
meteorites, we can infer many of the same properties for the asteroid
Apophis itself," Binzel says.

An object the size of Apophis (about 270 meters across) could devastate a
region as large as France, or produce tsunamis over a wide area if it
struck at sea. Many ideas have been proposed for how to deal with
such a threat, ranging from using bombs, lasers or spacecraft to nudge it
out of the way to blowing it to pieces while it is still far away. The
selection of the best course of action may depend of the physical
characteristics of the object, including its mineral composition.

--END-

Written by David Chandler, MIT News Office
Received on Fri 12 Oct 2007 01:24:32 PM PDT