Even small asteroids, like the one that recently exploded over Russia, can cause disaster. It caused thousands of injuries from the shockwave that blew out windows and shook buildings.
These are called "century asteroids" because they hit the Earth on average about once every 100 years. The space rocks generally go unnoticed because they explode over the open ocean, but if they hit a populated area it could spell disaster.
And as cities spread out and grow, these asteroids become more of a threat to humans. "We were blissfully unaware of the fact that we've had near misses and actual collisions with objects about the size of an apartment building," Kaku pointed out.
So far the asteroids we've encountered have been "city-busters," says Kaku. But in 2036 we will have a "nation-buster."
Kaku is referring the Asteroid Apophis, an asteroid 10 times bigger than the one that skimmed Earth earlier this month. According to Kaku, the asteroid will graze Earth's atmosphere in 2029. Depending on how much friction is created during that flyby, there is a window of opportunity that it could hit on its next pass in 2036.
What can we do? Experts have some dramatic plans up their sleeves.
Kaku says some plans include landing on a potentially hazardous space rock and placing a rocket on it to push it "slightly out of the way so that on the second pass it misses Earth."
An Armageddon-like tactic (exploding nukes in an asteroid) wouldn't work because blowing up a big, solid asteroid would just make hundreds of little baby asteroids that can spread out the damage making the impact equally, if not more, dangerous
Astronomers are also watching the skies for comets. Comet ISON, dubbed the "comet of the century" by NASA, will make its closest approach to the Sun in late November. If the comet survives, "it could emerge glowing as brightly as the Moon, briefly visible near the sun in broad daylight," says NASA.
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