Aren't the astronomers supposed to be watching the sky to let us know way before this happens??
Uh, hello..pay them more and they will do their job. Unless the astronomer was sitting there, at his telescope going.."hrmm...I don't think it will come close to earth". *hands graduate student the paper work to do. Graduate student comes back a day or so later. "uh, sir, you had a minor miscalculataion on the orbit of this asteroid." Thats when the OH SHIT comes in.