Thanks to a number of asteroid surveys, such as NASA's Center for Near Earth Object Studies, there is a healthy inventory of large asteroids. "We've found 95 per cent of all the really big, one-kilometre-sized asteroids," said Peter Brown, professor of physics and astronomy at Western University in London, Ont.
"We're going to know within the next couple of decades for sure if any time over the next century if there's an asteroid that's going to hit." Of course, there can't be an absolute guarantee that a smaller asteroid wouldn't impact Earth.
We got a dose of what a smaller one could do on Feb. 15, 2013 when a 20-metre piece of space rock exploded in the atmosphere over Chelyabinsk, Russia. Two minutes after it passed, an air blast shattered windows, injuring almost 1,000 people. Travelling nearly 70,000 km/h, it released energy equivalent to 30 Hiroshima bombs.
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