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Arizona astronomers discover nearest-to-Earth asteroid

Posted on: Thursday, 16 October 2003, 06:00 CDT

PHOENIX (AP) -- An asteroid discovered by Arizona astronomers last month passed within 52,000 miles (83,668 kilometers) of Earth -- the closest documented approach of an asteroid that didn't collide with the atmosphere.

Close encounters with asteroids of its size, about 3 meters to 6 meters (10 feet to 20 feet) in diameter, are not unusual, astronomers believe, but catching images and documenting orbits of those asteroids are difficult.

``The coup is to actually see one of them ... so we had a bit of luck,'' said Edward Bowell, director of Lowell Observatory's Near Earth Object Search program.

Images of SQ222, as it's been dubbed, were captured by Lowell Observatory in Flagstaff, Arizona, and documented by Fountain Hills-based nonprofit Minor Planet Research.

Minor Planet Research was testing a computer and image system designed to allow students to look for asteroids and other space objects when a researcher spotted three small white lines, images of an object moving about twice the speed of the moon.

The discovery was relayed back to Lowell and the Minor Planet Center, a Cambridge, Massachusetts-based Smithsonian Institution program, which asked other astronomers for help spotting the asteroid.

Using data from other observers and another sighting at Lowell, astronomers have been able to project the orbit of SQ222 and calculate how close it passed to the Earth, said Brian Marsden, director of the Minor Planet Center.

``It has made the closest approach to the Earth of any known asteroid in space,'' he said.

SQ222 passed 52,000 miles (83,668 kilometers) from the Earth, less than a quarter of the distance to the moon, on Sept. 27. Before its discovery a day later, the closest documented pass was about 65,000 miles (104,585 kilometers), Marsden said. That asteroid, spotted in 1994, was slightly bigger.

Based on observations of SQ222 and subsequent calculations, Bowell said it does not appear that the asteroid will pass close to Earth again for at least another decade.

Had it struck the Earth's atmosphere, it likely would have simply burned up. ``It is a very tiny object,'' Marsden said.

Astronomers are most interested in discovering and documenting the orbits of large asteroids, especially ones with any potential to damage Earth.

But the discovery of even small asteroids can help researchers better calculate the total number of asteroids. ``You never know what you're going to find, and you're never going to find anything unless you look,'' Bowell said.

Paul Johnson, executive director of Minor Planet Research, said the discovery of SQ222 helps illustrate the importance of the human element in searching for asteroids and other space objects.

To save money and time, most asteroid research is done using computers with set parameters designed to identify objects, but Minor Planet Research's asteroid discovery system adds the human eye to the equation, Johnson said.

The nonprofit hopes to have the system installed at the Challenger Space Center, an education center in Peoria, Arizona, near the beginning of the year so that students will have a chance to make their own discoveries.

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On the Net:

Lowell Observatory: http://www.lowell.edu/

Minor Planet Research: http://www.minorplanetresearch.org

Smithsonian's Minor Planet Center: http://cfa-www.harvard.edu/iau/mpc.html

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