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Inspired by the doomsday headlines, Internet posters and late-night monologuists made lame jokes about the futility of long-term insurance policies and the new significance of 30-year mortgages. The news was not lost on Washington, where Jim Kennedy, special adviser to the White House counsel, revealed that Clinton insiders had chosen their own name for the asteroid: "Ken Starr's backup plan."
Then, as abruptly as the asteroid mania began, it was over. Jet Propulsion Lab astronomer Eleanor Helin, rummaging through some photographic plates taken in 1990, found previously overlooked images of XF11. Combining the asteroid's position eight years ago with the current readings, three groups working independently arrived at the same conclusion: the miss distance was actually 600,000 miles, and the chance of XF11's hitting Earth in 2028 was zero, or as JPL astronomer Don Yeomans declared, "less than zero."
The worldwide sigh of relief was almost palpable. The threat of asteroid strikes, however, still looms over the planet, which has been hit many times in the past by large objects raining down from space. Evidence of these ancient impacts is everywhere: more than 150 craters pock Earth's surface, some clearly visible, some that can be seen only from aircraft or satellites, others long buried or on the ocean bottom.
By far the most notorious of these craters is the circular feature 120 miles in diameter discovered below the northern tip of Mexico's Yucatan Peninsula. This monster crater is believed to be the impact site of a six-to-eight-mile-wide comet or asteroid that struck 65 million years ago and wiped out the dinosaurs and some 70% of Earth's other species.
While these catastrophic events seem remote and unreal, there are plenty of more recent reminders that Earth's neighborhood in space is still teeming with mountain-size rocks and the occasional wayward comet. Arizona's spectacular Meteor Crater, for one, was gouged out only 50,000 years ago by an iron asteroid. The impact and explosion blasted a hole nearly three-quarters of a mile across and 700 ft. deep. Today it could destroy a city.
Much more recently, in 1908, an asteroid or a chunk of a comet less than 200 ft. across roared into the atmosphere and exploded some five miles above the unpopulated Tunguska region of Siberia. The blast, estimated at tens of megatons, devastated an area of several hundred square miles, knocking down trees, starting fires and killing reindeer. Had it occurred over a large city, hundreds of thousands would have died.
And two years ago, an asteroid about 1,500 ft. across was discovered just four days before it sped by at 58,000 m.p.h., missing Earth by only 280,000 miles. If it had hit, the resulting explosion would have been in the 3,000-to-12,000-megaton range--equivalent, as the late astronomer Gene Shoemaker put it, to "taking all of the U.S. and Soviet nuclear weapons, putting them in a pile and blowing them up."
Scientists agree that it is only a matter of time before another celestial hulk hits home. "It's like a game of cosmic darts," said astronomer Clark Chapman on the PBS show Nova. "It could just as likely happen tomorrow as some day 300,000 years from now."