I got to thinking about asteroids, and the possibility of an asteroid or comet striking the earth. It seemed relevant, so I thought I'd share it. If such an asteroid were spotted the process to save the earth would be pretty clear. We send a spacecraft to intercept it, plant some kind of charge against it, and divert its path by a tiny amount - possibly a small fraction of a degree. The difference is minimal, but by the time the comet reaches the earth's orbit it's moved far enough ...