What is the Best Way to Defend the Earth from an Asteroid Impact?
In considering the challenge of asteroid impacts, it’s first important to keep the probabilities in perspective. If it were likely for humans to be wiped out by an asteroid impact, it would probably have already happened in our 2 million+ year history. Asteroids larger than 25 m (82 ft) in diameter impact us more rarely than once per century, and appreciable amounts of the asteroid fail to even reach the surface. The effect of such an asteroid impact is an airblast about the size of a small atomic bomb. Human cities only cover a minuscule fraction of a percent of the planet. If an atomic bomb (or atom-bomb-sized impact) occurred at random somewhere on the planet, the likelihood of it killing anyone would be less than one in a million. In more than 2000 years of recorded history, no asteroid impact has killed even a single person. Somewhat more serious than the small asteroids which continually impact the Earth are asteroids larger than 250 m (820 ft) in diameter, which impact the Earth
