June 29, 2010

Lawrence Livermore Simulating Viable Nuclear Bomb Asteroid Deflections

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There have been disagreements about the best way to deflect asteroids. There is option of a nuclear bomb or gentler non-nuclear methods. David Dearborn, a research physicist at the Lawrence Livermore National Laboratory in Livermore, says that if an asteroid was expected to collide with Earth within the next 50 years, using nuclear explosives to divert or disperse the hostile space rock could be the best alternative.

The nuclear bomb is the strongest bomb we know," said Dearborn, who presented his study last month at the 216th meeting of the American Astronomical Society in Miami, Fl. "It's about 3 million times more efficient than chemical bombs. The question is how to use that energy."

The interloping space rock would have to pose a definite asteroid threat to Earth in a relatively short timeframe to justify such a drastic option, the scientists said. And blowing up an asteroid runs the risk of creating more debris to worry about later

"If we have an asteroid that is really large, and we don't have more than a few years notice, nuclear is probably all we can do," Morrison told SPACE.com. "If it's a mile or smaller and we have 10 to 20 years warning, we probably won't go nuclear." In such cases, scientists could opt to impact the asteroid with a ballistic rocket, sending the cosmic interloper off course.

Dearborn discussed a previous proposal to use a powerful laser beam to repeatedly zap an asteroid in order to alter its course. While this could be a feasible option, Dearborn said, the timescale needed to carry out such an operation using current technology is too large.

For example, using a beam from the National Ignition Facility to deliver enough energy would require 5 million pulses which would have to be delivered over the course of approximately 6,000 years.

To effectively fragment and divert an asteroid, its orbit must be pushed by at least a centimeter per second. To do this, about five to 10 kilotons of energy input is needed, regardless of the method.

"The nice thing about any kind of intervention is that you only have to make it miss the Earth," Dearborn said. "A very small change in its orbital period will do that."

Dearborn created simulations to examine the amount of energy and time needed to most effectively divert an asteroid and disperse its debris field in such a way as to minimize collisions with Earth.

He found that intersecting a 270-meter body asteroid with a 300 kiloton energy source at the surface could safely be done 15 days out from impact.

"If you can intersect it 15 days out, which is beyond the orbit of the moon, that would be fine," Dearborn said. "It was enough that 97 percent of that material missed Earth."

Furthermore, if the explosion occurs far enough into space, debris should be less of a concern, said Morrison.

"If you're going to do this 100 million miles away from Earth, it shouldn't be too much of a problem," Morrison said. "There'll be a little bit of debris, but by the time it gets close to us, it would be pretty dispersed

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