they hype up the power of all the nukes in the world but i'm pretty sure a 1km diameter rock that is certain to collide with us would not be able to be bumped off course with all those nukes, and blown up right next to it out at pluto... the weight alone is immense, and then add the velocity of thousands of meters per second

but it's fairly unlikely considering it's a pretty tight window when you count that our planet is flying around the sun at 400m/s