I just watched it now. I left a
review in the movie thread (conclusion: strong first half, weaker second half, some distraction, so overall a bit uneven), but I am amazed how a lot of reviewers seem to think a movie like this could have really changed something, if only it would have been more subtle. If the climate change debate shows anything, it's that it is very difficult to change people's minds on the subject, and you really can't expect that from an allegorical satire. This film 'just' laughs at the insanity of the world - it's not a sermon. Changing minds would have required an entirely different film, one that you could never expect from Adam McKay. So maybe what's really implied by the comments of those reviewers, is that there is a surprising lack of films about climate change - and hence when finally there is one, it has to be everything at once.
There are now actually things in place to deal with such a comet.
As the film says, NASA's
Planetary Defense Coordination Office is a real thing, and I suppose they don't work alone (there is already a reference to ESA in the article I reference below). First, there are programs that constantly watch the sky to map object trajectories (comets, meteoroids, whatever else) and detect potentially dangerous ones. It would therefore be actually very unlikely that a grad student looking for other stuff would coincidentally be the one finding a 'planet killer'. Once that's detected, rockets would be fired to attempt to nudge the object off its current trajectory. In fact, as it happens, two months ago a rocket was launched that will connect with an asteroid in the fall to test this approach - see
here.
So no, we wouldn't just panic and die. Or at least, not until the nudge fails.
I know you didn't ask me, but one issue I had with The Big Short (which I thought was otherwise very good), is that the main characters come out on top, and that's not presented as a bad thing. I felt to me like the ending said 'good on them that they saw the issue and played the system to come out on top', which is very frustrating given how the movie otherwise demonstrates how problematic that system is, and that the sort of thing that made the main characters all that money is deeply wrong.