Asteroids like the one that traced across the Russian sky last year pound Earth on a regular basis, according to new data from a system used to detect nuclear weapons explosions -- and there's no telling when the next one is coming. “Because we don’t know where or when the next major impact will occur, the only thing preventing a catastrophe from a ‘city-killer’-sized asteroid has been blind luck,” said B612 co-founder and CEO Ed Lu, a former NASA astronaut.
