A huge asteroid is expected to fly by Earth later today. Astronomers say the space rock the size of a delivery truck will make one of the closest approaches ever, but NASA said yesterday there's no risk of it actually hitting Earth. It's expected to be 22-hundred miles above the southern tip of South America, about ten times closer than some communication satellites, when it buzzes past. NASA puts the asteroid's closest approach at 7:27 p.m. Eastern Time.