Tracking the Asteroid Threat

April 25, 1992

Here's something to worry about: A small asteroid -- a chunk of space debris perhaps a half-mile in diameter -- is on a collision course with Earth. A strike by a body that size could explode with the force of 25,000 hydrogen bombs, creating massive tidal waves and flinging enough dust into the atmosphere to block out sunlight for months. Civilization would collapse. Anyone who survived the initial impact would shortly die of starvation or exposure. Eventually all traces of human life would be extinguished from the planet.

Scientists say the chances of such an event occurring tomorrow are extremely small. But the Earth has been struck repeatedly in the past by objects whose orbits around the sun periodically cross its own. Evidence of such events are preserved on the Moon's cratered face; erosion on Earth has mostly erased the geological record, although relatively recent events, like the meteor impact that carved out the great Crater Lake in Oregon 60,000 years ago, are still visible. Early in this century a comet is thought to have exploded over Siberia, felling trees over a 100-mile radius. And scientists suspect the impact of an asteroid or comet may have been responsible for the extinction of the dinosaurs some 65 million years ago.

In 1989, a half-mile-wide asteroid flew through Earth's path, missing our planet by only about 500,000 miles, or twice the distance to the Moon. That close call prompted Congress to convene a NASA team of 100 scientists to study the threat posed by such objects. The group reported the chances of a large object hitting Earth were on the order of once every 300,000 to 1 million years -- hardly reason to fear imminent disaster. But it did recommend setting up a network of six small telescopes with computerized detectors capable of picking out fast-moving asteroids as they whizzed past the backdrop of stars. If any threatening object were out there, the network would provide decades of warning.

One bonus of the project is that the system almost certainly would make other discoveries unrelated to its original mission. And the cost of such a network would be relatively low -- only about $10 million. All in all we think that's a small enough price to pay for prudent science -- not to mention a little peace of mind.

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