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@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