In the unlikely event of a gigantic asteroid threatening mass extinction on our planet, scientists are now confident such a disaster could be averted using nuclear weapons. Researchers running new and sophisticated simulators conclude it would take as little as 5 to 10 kilotons of energy to divert an asteroid. That's a relatively small nuclear weapon.
"The nice thing about any kind of intervention is that you only have to make it miss the Earth," said David Dearborn, a research physicist at the Lawrence Livermore National Laboratory. "A very small change in its orbital period will do that."
It might not even require that kind of conflagration if a threatening asteroid is a few years away. In that case, a well-aimed missile could divert a space rock just enough to make it miss the Earth. Or maybe they could use that "gravity tractor" British scientists were talking about a few months ago.
But what about all the resulting debris from an exploded asteroid? Won't that still cause a lot of damage? If the asteroid is blown up 100,000,000 miles away, the debris will be so dispersed it won't hurt us. If it's about 15 days away, it would take a 300-kiloton bomb to obliterate an asteroid about 1000 feet in diameter, with only a small percentage of the debris still reaching the earth, and probably burning up in the planet's atmosphere.
You can rest easy, though. Although there will almost certainly be a cataclysmic impact with Earth sometime within the next million years or so, that happens to be a long, long time, making the chances of an impact within our lifetimes somewhere between slim to none.