Journey Into Space: Gravity, Orbits, and Collisions
Space Astronomy and Space
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Blast It! (Maybe Not)

An asteroid is on a collision course with Earth. All life as we know it is in jeopardy. Hollywood's ready answer: Send a crew of astronauts to plant a nuclear warhead deep inside the asteroid and blow it up. At least that's the gimmick in last summer’s meteoric flicks “Deep Impact” and “Armageddon.”

But is it really our best shot? Hardly. "Blowing up an asteroid is the worst thing you can do," says Donald Yeomans of NASA's Near-Earth Object Program Office in California. "Then you've got a shotgun blast instead of a bullet." In other words, nuking one huge chunk of rock might blow it into smithereens, but it could also unleash a torrent of shattering debris headed straight toward us on Earth.

A safer bet may be to gently nudge the asteroid "a few millimeters a second," says Yeomans. His scenario: First, NASA would learn to identify any Earth-threatening object a decade or two prior to impact. Then, NASA might send an unmanned spacecraft to set off a nuclear blast in space, right in front of the asteroid, but not directly on its surface. The blast would vaporize the front side of the asteroid, but would nudge its orbit out of harm's way. "The resulting rocket-like thrust on the asteroid slows it down enough so that in 20 years or so, it will miss the Earth," Yeomans explains.

But what if we had, say, only six months warning? The possibility may be unlikely, but so far scientists have tracked only 10 percent of potentially hazardous near-Earth objects. "I doubt there's a ready solution or any ready hardware," says Robert McMillan, an astrophysicist with the Lowell Observatory NEO Survey program in Flagstaff, Arizona. In other words, duck!
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