Research presented by MIT graduate student Scott Stuart at a meeting of the American Astronomical Society's Division of Planetary Science showed that because the inclinations -- angles of orbit in relation to the plane of the Earth's orbit around the sun -- of known NEAs are not representative of the entire population, there may be more undetected NEAs out there.

NEAs with low inclinations are easier to find than highly inclined NEAs, Stuart noted. Thus, the known NEAs tend to have low inclinations rather than being representative of the population.

With the new determination of higher inclinations for the NEA population, researchers at MIT Lincoln Laboratory now estimate that there is a mean total of more than 1,100 near-Earth asteroids bigger than 1 kilometer (0.6 miles) in diameter. Recent estimates had ranged from 750 to 900. Those prior estimates used a small number of asteroid detections and assumed that the NEAs have lower inclinations than suggested by Lincoln Near-Earth Asteroid Research (LINEAR) Project data.

This new number is consistent with earlier estimates of the population made by the late astrogeologist Eugene Shoemaker, who based his analysis on the number of asteroid impact craters on the moon.

NEAs are objects within our solar system whose orbits may bring them close to the Earth. While no currently known NEAs are now on a collision course with the Earth, many NEAs remain undetected.

The amount of damage that would be caused by an asteroid depends on its size. Asteroids bigger than 1 kilometer are thought to be capable of causing extensive damage on a global scale.

Astronomers find and catalog asteroids by imaging large swaths of sky with telescopes and searching for objects that move against the background of fixed stars. By tracking an asteroid's location over several months, astronomers can calculate the orbit that the asteroid follows and determine whether it could pose a hazard to the Earth.

LINEAR has been scanning the skies to discover and catalog NEAs and to provide advance warning if any are bound for Earth. Since March 1998, LINEAR has found 70 percent of all near-Earth asteroids discovered worldwide. It is a major contributor toward NASA's goal of cataloging 90 percent of NEAs larger than 1 kilometer within the next 10 years.

No one yet knows exactly how many NEAs are out there. However, it is possible to make estimates of the number remaining to be discovered based on the number already found and the amount of searching that has been done to discover them.

LINEAR has detected more than 400 different near-Earth asteroids. This ten-fold increase in detections has allowed researchers to investigate more accurately the inclination distribution of NEAs.

Stuart is a participant in the MIT Lincoln Laboratory Scholars program, an employee education program, working with Richard Binzel, professor of Earth, Atmospheric and Planetary Sciences at MIT, and a member of the LINEAR project team. Principal investigator of the LINEAR project at Lincoln Laboratory is Grant Stokes, assistant division head.

The LINEAR project, conducted by MIT Lincoln Laboratory, is jointly sponsored by NASA and the United States Air Force.

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