Scientists ponder how Earth can duck an asteroid


MOUNTAIN VIEW, Calif. -- The chance that the Earth will be struck by a milewide asteroid in the next year is greater than the chance that any given person will be struck by lightning -- about 1 in a million. But since an asteroid that size could destroy half the planet's population, some NASA scientists say it's a statistic worth worrying about.

"We know that the Earth exists in a swarm of comets and asteroids," David Morrison, chief of the Space Science Division at NASA's Ames Research Center here, said last week.

About 10,000 asteroids have orbits approaching the Earth, and tracking them would require at least six telescopes with 2-meter to 3-meter mirrors distributed throughout the Northern and Southern hemispheres, Mr. Morrison said. As chairman of a 23-member committee of astronomers commissioned by Congress to study the potential problem, Mr. Morrison will ask Congress later this year to support a thorough comet- and

asteroid-tracking project.

The six telescopes would cost about $12 million apiece, Mr. Morrison said.

Using smaller telescopes in the United States and Australia, astronomers are now tracking one or two comets and asteroids a month.

Although there is a slim chance that a giant asteroid could strike the planet at any moment, Mr. Morrison says that with proper tracking techniques, astronomers could spot a catastrophic one decades before it would hit the Earth.

The next step would be to meet the meteor, deflecting it from its collision course.

"The simplest way, we think, to give it a shove is to set off a nuclear bomb next to it," Mr. Morrison said, explaining that changing the asteroid's speed by even 1 centimeter a second could avert catastrophe.

If the telescopes could enable astronomers to see the deadly meteors years before they would hit the Earth, scientists would have time to develop the technology to stop them, Mr. Morrison said.

An asteroid a mile in diameter would hit the Earth at about 15 miles a second, producing an explosion akin to a million megatons of TNT. Dust and particles produced by the blast would block about 90 percent of the sun's rays and lower the planet's average temperature by 10 to 20 degrees for several months.

Scientists say all the world's crops would be destroyed for an entire year, causing half the population to die of starvation.

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