In 2007 NASA presented the United Sates Congress with 3 plans to save the Earth from a potential asteroid collision. The need for 3 separate plans comes from the different natures of asteroids but rest assured, should the threat arise, NASA have you covered.
1. The Slow Push Plan
The goal for the slow push plan is to essentially knock an asteroid out of orbit, NASA determined three ways this could be done. Ablation involves using a huge mirror to focus a massive beam of sunlight onto a particular spot on the asteroid. This would generate a large amount of heat, vapourising material and creating a jet of gas and debris on the surface of the rock. This would slowly push the asteroid onto a different path and out of Earths way.
A Gravity tractor is a massive spacecraft that when flying past an asteroid would cause it to be pulled out of orbit by gravity. Then there’s the space tug, which involves a spacecraft being attached to the asteroid and using propulsion systems to move the entire asteroid away from it’s collision course.
All of these slow push plans have issues, the main one being that none of the spacecraft actually exist, but that’s why there are two other back ups.
2. The Kinetic Impact Plan
This plan is described by NASA as the most mature idea, utilising a delta 4 rocket with a high density impactor attached, something along the lines of uranium that will really make a bang and blow the asteroid up.
There are of course limitations to this seemingly simple idea. Many asteroids are actually dense clouds of rubble held together by gravity and so blowing them up would create many small asteroids that would still collide with Earth. So it works for some cases, but not massive rocks, hence the third and final plan.
3. The Nuclear Plan
A small megaton neutron bomb would divert the path of a large asteroid a hundred times better than any other option. Obviously there is a worldwide ban of the use of nuclear weapons in space, but we’re hoping the world would cooperate if the other option was obliteration.