Ok. I can see why.Andrew,
The mechanism is not the bomb mass hitting the asteroid.
The mechanism is that the radiation from the bomb ablates the material of the
asteroid itself, and the blowoff of that material is what gives the asteroid the
That would require putting the bomb inside the asteroid. I suppose that you could have a bunker buster type of bomb blast into the asteroid and then detonate the nuclear bomb. That might work but you would need to blast a large portion of the asteroid and you would need a very large nuclear device.