•what is one way that we could defend earth from asteroids? what are the drawbacks of the method?

Kinetic impactor is one way to defend earth from asteroids. However the drawbacks are that kinetic impactor can deflect the asteroid in only one direction.  

Explanation:

Kinetic impactor is a high-speed spacecraft that is sent into the space to deflect the approaching asteroids that are near to earth. The process of deflection would cause crashing of kinetic impactor inside asteroid to change its trajectory so that it’s much far off earth’s orbital path. The drawbacks are that it is a slow process and all it can do is to divert it in one direction, that too only westwards and not destroy the asteroids completely. Not only that, kinetic impactor may be effective in deflecting smaller asteroids, but they will surely not be effective in changing orbits of much larger asteroids.