The momentum of the whole system would likely be similar, but it'd be spread over a much wider debris field - in the case of an asteroid impact, a field probabl

The momentum of the whole system would likely be similar, but it'd be spread over a much wider debris field - in the case of an asteroid impact, a field probably large enough that much of it would completely bypass instead of impacting. From a practical standpoint, anyone debating between nuclear and non-nuclear options would probably have to look at the risks of a more complex projectile (reliability), whether an explosion would allow use of a smaller projectile (energy cost for getting there, terminal speed, accuracy at various speeds), and of course regulatory concerns with launching nuclear vs kinetic impactors.