A Tiny Asteroid Whizzes By

On Saturday, September 27th, a very small asteroid plunged past Earth well inside the Moon's orbit. Unseen, it passed just 78,000 kilometers (a fifth the Moon's distance) above Earth's surface before barreling back into interplanetary space. Judging by its faintness — 18th magnitude when first picked up the next day — it can't be any larger than 3 to 6 meters across. That's "SUV or room size," notes Edward L. Bowell, principal investigator for the Lowell Observatory Near-Earth Object Search (LONEOS) at Anderson Mesa, Arizona, where the first images were taken.

LONEOS collaborates with Minor Planet Research, Inc., where Robert A. Cash used the PinPoint detection software to discover the object's faint trails on three LONEOS images. He immediately sent his measurements to the Minor Planet Center in Cambridge, Massachusetts, which alerted astrometric observers around the world.

More images of the rapidly receding, fading object were acquired on the 29th by LONEOS, and also by amateur astronomer Peter Birtwhistle in Berkshire, England, using a Meade 12-inch Schmidt-Cassegrain telescope. The Minor Planet Center announced the find on October 1st, dubbing it 2003 SQ222. Brian G. Marsden's orbital elements, refined on October 3rd, indicate that the tiny planetoid is traveling in a low-inclination orbit that takes it to well out beyond Mars's distance from the Sun, then inward as close as Venus, in a period of 1 year 10 months.

If it ever hits Earth it should break up in the upper atmosphere, causing virtually no harm — much like the slightly smaller Park Forest meteorite that dropped fragments on a Chicago suburb last March.

Asteroid 2003 SQ222 now tops the Minor Planet Center's list of the closest known approaches by asteroids outside the Earth's atmosphere. But larger objects have come even closer. Meteor Crater near Flagstaff, Arizona, was produced by the prehistoric impact of an asteroid perhaps 1,000 times more massive than 2003 SQ222. The meteoroid that exploded over Tunguska, Siberia, in 1908 may have been 30 times wider than 2003 SQ222. When hundreds of tourists saw the great Grand Teton National Park fireball of August 10, 1972, they were witnessing the atmospheric graze of an object about twice the size of 2003 SQ222 before it skipped back into space.