Wouldn't nuke going off just next to it nudge anything enough off course to not have to worry about composition? Or Hollywood yet again inserted a very unrealistic picture of how things work in my head.
Or we strictly prefer not sending nukes up there outside WWIII scenario. But then plenty of satellites have/had nuclear fuel as main source of energy, just not critical mass for anything BAM, just nasty dispersion in the upper atmosphere threat.
A nuke going off "near" anything in space will do very little damage - there's no shockwave propagation, so all you have is the bombs heat - which at least half gets wasted on empty space.
One of of the big problems with nuking asteroids is, as in this case, if it's a rubble pile then it can be considerably difficult to get enough physical contact with it to even meaningfully effect it.
Hence the reason for DART: we've got an impressive something but the question is did we even successfully deflect the trajectory of the bulk of the material?
Or we strictly prefer not sending nukes up there outside WWIII scenario. But then plenty of satellites have/had nuclear fuel as main source of energy, just not critical mass for anything BAM, just nasty dispersion in the upper atmosphere threat.