“Lucifers Hammer”
by Larry Niven
Great book.
Except that Hamner-Brown was a comet, not an asteroid. Comets are usually much bigger, and more likely to throw debris into the atmosphere. A land-striking nickel-iron asteroid, up to 100-200 meters, would make a heckuva hole, but nothing like a comet strike. Hitting the ocean, on the other hand, would probably be the same for a comet or asteroid. Now, a bigger asteroid, like 500 meters or more, and it’s game over.
Great book. IIRC Niven did it alone and not in concert with Gerry Pournelle. They worked wonderfully together on many books, espeially Footfall.