Is the nuclear weapon our last defense against alien invasion?
A nuke probably wouldn't be that effective. Because a nuke mostly works by blast effects, which are greatly helped by the atmosphere, and as you'll recall in space there is no atmosphere. Then, these guys came from another star system, presumably quite fast, so presumably have some form of shield against radiation which would also mitigate against many of the effects of a nuclear explosion.
The current thinking in some circles is that we hit them with a couple of thousand tonnes of metal launched from a thunderwell, which is basically a hole in the ground with a nuke at the bottom, filled with water, which turns to steam on detonation, which launches a big dumb mass into orbit, which can be aimed at the mothership and which would cause significant impact damage when it hits them. What could possibly go wrong?
Potentially, quite a lot. Presumably they could move out of the way if they saw the big dumb mass coming, or shoot it down with their meteor defence system which they're likely to have.
/. I assume we'd launch our possibly stealthed big dumb mass to the same orbit as the mothership but in the opposite direction so as to obtain the maximum collision velocity. Or maybe a shotgun pellet effect would be more efficient, if they have some kind of point defence system...