[Roanon]

Originally posted by oleg:
but insted we will have a stream of sublight-speed particles that are no longer opposed by atmosphere density. We will still have the same sort of "front wave", now propogating with the speed of light. If you remember from nukes explosions, staff around the center was evaporated. It is caused by photons, not a shockwave !

Well, if you think of sublight-speed particles, you should certainly not select photons . Also, there is relatively few resistance to them (or other particles) from atmoshpere density, at least here on earth. Not even on Jupiter. Except on diskworld, I have not yet seen light been slowed down by air .
If you mean alpha particles, neutrons, or anything else like that - the evaporation of the staff in the center may be caused by them, but not via measurable concussive force. This is matter destruction on a molecular/atomic level, and while you may be able to turn a small portion of said asteroid into dust its course will not be affected in any way.