The interesting part is that we KNOW already (documented by the US KillSats that constantly scan for nuclear explosions on the planets surface) that
small asteroids of about 10-30 meteres diameter often impact the upper atmosphere. Most times, they detonate with the yield of megaton nuclear
weapons, and on average about 5 impacts occur per year.
It's not just the big asteroids we have to watch out for—the little rocks can be dangerous too. They're hundreds of them out there and they're hard
to spot, but NASA has decided it had better start searching for them.
Robert Roy Britt writes in Space.com that it will cost at least $236 million to add a search for small asteroids to their ongoing Near Earth Object
(NEO) detection program. An asteroid twice the size of a football field or bigger hits the Earth about every 15,000 to 20,000 years, according to
NASA's Donald Yeomans. Impacts from smaller space rocks cause only regional problems, but these could be severe, and there are so many more of them
that this kind of impact is much more likely to occur.