A Near Miss From Outer Space

Earth received a cosmic calling card last week. It arrived in the form of a huge rock, about 1,000 ft. in diameter, that hurtled past the planet at 68,000 m.p.h. The asteroid, newly dubbed 2001 YB5, missed us by some 500,000 miles, about twice our distance from the moon. For astronomers, however, that was a hairbreadth, and a dramatic reminder that space is filled with debris that has devastated our planet in the past and could very likely to do so again.

Had 2001 YB5 been on target, says Donald Yeomans, a senior scientist at the Jet Propulsion Laboratory, it would have struck with the explosive force of some 4,000 megatons, enough to obliterate a major metropolitan center and the surrounding countryside. But what troubles most scientists is that the asteroid was detected only two weeks before it flew by. If it had been headed toward impact, those in the target area would have had barely enough time to write their wills. Eleanor Helin, whose Near-Earth Asteroid Tracking group discovered the asteroid, estimates that, on average, one object the size of 2001 YB5 or larger passes close by annually; many such asteroids are undetected. Her goal, and that of the other asteroid hunters, is to identify the intruders, plot their orbits and predict possible impacts further in advance. That might just provide enough time for measures to deflect or destroy the menace before catastrophe strikes.

--By Leon Jaroff