a) 0% of stopping it. 100% of it occurring again at some point. b) No c) Irrelevant Nope we couldn't save ourselves. That's why it's called an extinction l

a) 0% of stopping it. 100% of it occurring again at some point. b) No c) Irrelevant Nope we couldn't save ourselves. That's why it's called an extinction level event. If you have say a 50 km^3 asteroid on a course to earth (about 1/10th the size of Vesta) there is little we could do on short notice. It might be another story if we had a long time to prepare. For example if the asteroid had a favorable composition, we could try drilling into it for a decade or two, in the hope that we could explode a nuke in a carefully engineered hole to try to alter it's course without breaking it.