Is there NO other way to write this?
Amateur astronomer finds it, frantically phones it in, military rushes around, needing stuff "NOW!" or "yesterday!" The president doesn't want to panic the people. Small catastrophes ensue, to people we're supposed to be rooting for because they show us the drama in their life. A mission is planned, montage of training, they go up, things go wrong, people sacrifice themselves, planetary disaster averted at last second. Much rejoicing.
Just once, I'd like to see them (us) have no chance, and actual extinction occurs. But that's not a Hollywood happy ending.