The science is relatively straightforward when it comes to planetary defense. If you have enough time, you deflect it. If it's too big, you'd have to use something else. But the real hard thing is who gets to decide who runs this? Like if an asteroid was going to hit a state in the US or somewhere in the US, how do you convince an entire US state to evacuate? That's the ultimate unanswered question here of like less scientific and more and more political. Some things are always going to be unknown until they actually happen.