An asteroid came uncomfortably close to Earth in July. Could we have stopped it?

In July of this year, an asteroid roughly 30 to 60 meters across passed Earth to within one-quarter of the distance to the moon. It posed no threat to our world, but if it had struck Earth it would have created a blast three times greater than the 2013 Chelyabinsk impact. And we only noticed it two days after it passed.