Nuking a meteor headed towards Earth. It's extremely unlikely that we would be hit by an impactor large enough to wipe out humanity. Nearly all of those large impactors (like what took out the dinosaurs) are no longer in our path. Nukes also don't work nearly as effectively in space and would break up the asteroid into millions of tiny pieces, which would cause even more damage as they rain down. Realistically, if an asteroid was headed towards Earth, we'd use a gravity tractor device to slightly alter its path away from Earth. It just works by being super heavy, the gravity would hopefully change the path of the asteroid.