Since I haven’t seen this question answered yet - no offense to those who have tried; you do bring up good points- I’ll throw in my two cents. The question that was posed asked about the leading way to prevent an asteroid from colliding with the Earth. I am no NASA scientist, but I’ll throw out an idea I think should be near the top of the list. I make no claims that I’m the first to offer this idea. On the contrary, I’m sure it has been considered. I have never heard it proposed, but I am still not taking credit for the idea.
Background
We have all heard of Armageddon-prevention ideas such as blowing the asteroid up with a laser or nuke, veering it off-course, etc. However, all of these ideas seem to assume that a moving object is on a collision course with a stationary one. Of course, we all know this is not the case. The Earth is obviously in a constant elliptical orbit around the Sun, while the asteroid is in some other course of motion. So, for a collision to take place, an asteroid’s trajectory would have to intersect Earth’s orbit. Further, the Earth must also be located at or near that intersection point at the exact time the two trajectories will be intersecting.
Idea
If an object in space is predicted to crash into Earth, both of these points must be true. So, how do we prevent a collision? We don’t have to blow the asteroid to bits, even though it may be fun. We don’t have to push it sideways enough to avoid Earth’s orbit. All we really have to do is speed up or slow down one of the two objects- Earth or the asteroid. Since we obviously do not want to alter Earth’s orbit around the sun, and because Earth will be orders of magnitude larger, we’d chose to alter the asteroid’s speed. If we sped up or slowed down the asteroid, its trajectory may still intersect Earth’s orbit. However, it will do so when the Earth is at a different location in its orbit, and thus avoid collision.
A big issue with this idea is the question of how to alter the speed of an asteroid. One approach would be to land a rocket on the asteroid, secure it, and use its thrust to speed the asteroid up or slow it down. It would probably take many years and rockets to alter the speed enough to avoid a collision, so early detection is a must. You may wonder why we wouldn’t just push the asteroid sideways instead of altering its speed, and you may be correct. I’m just throwing out a different way to view the problem. You may also argue that if we don’t deflect or destroy the asteroid, it may still wander too close to Earth for comfort. To that point I’d respond that at least we’d continue living, which sounds wonderful to me.
