On Nov 17, 5:40*pm, wrote:
"Scientists have given some thought as to how we'll
defend ourselves when a giant asteroid inevitably
heads our way and solutions range from paintballs
to nukes. A team at Iowa State University has settled
on the latter, and they've got plans for ship to do it
waiting in the wings."

See:

http://gizmodo.com/5961485/meet-the-...spacecraft-tha...

blowing up asteroids is a bad idea creating much more debris over a
wider area, doing more damage than a single impact