If the asteroid is far enough away, blowing it apart, even partially, would change all trajectories to almost certainly miss the absurdly tiny target that is th

If the asteroid is far enough away, blowing it apart, even partially, would change all trajectories to almost certainly miss the absurdly tiny target that is the earth from a distance of tens or hundreds of millions of miles away. On the other hand, if it happened close enough to Earth that all the little pieces, even if very tiny individually, still fall into the atmosphere, their evaporation friction would roast our world's surface for minutes to hours, terribly, causing global extinctions despite there never having been a single major impact at all. The movie Deep Impact badly fucks that last scenario up near its end when humanity is saved by the main asteroid being completely blown apart just hours away from impact with the Earth. In reality, there'd have been no literal deep impact, but the'yd have all died anyhow, literally baked to death along with every other flammable thing on the earth's surface.