Defense of Earth: what can be done?

W
hat if we find a large body headed our way?

Explosion

Let's first consider the hypothesis of making the object explode, with a detonation on its surface (or in its inner layers) obtained making a rocket collide with the body.

The possibility of destroying a potential impactor, probably with nuclear weapons has been studied in some detail. But with the current lack of detailed knowledge of the exact composition and structure of asteroids and comets, there are many doubts about the odds of this method.
A big danger comes from an incomplete destruction of the body. In this case, the Earth would be subjected to multiple impacts from the pieces that broke off from the original body, leading to a much bigger threat. If asteroids are generally made of loosely aggregated material, this scenario is much probable, and this choice could lead to a deadly shower that could cause an even greater damage than the initial body. For this reason, if an asteroid (or a comet) is found heading our way, telescopes observations, earth based radar and possibly space missions would be necessary to study the body composition.

 

Deflection

If the potential impactor were identified early enough, it could be deflected, or in other words, its orbit could be modified sufficiently to eliminate the possibility of the impact.
But the strength of this modification (how much the orbit needs to be modified) is inversely proportional to the period of time available before the impact. It has been calculated that under a 10 years' notice, nothing or very little could be done. Having a 50 years' notice, a spacecraft could deploy a rocket that would explode near the asteroid, blasting the object out of the way. Even in this case, it is not sure that the most powerful weapon available today could save Earth. At a too short notice, the use of nuclear weapons has been suggested to deflect the body. The story changes totally having a long enough period of time to organize the defense: having a 100 years' notice, even a very modest explosion near the asteroid could be enough to deflect it, changing its trajectory to a non-dangerous one.

Other means


Solar panels, a mean of deflection?
Courtesy of SSI

Some much gentler alternatives to explosions have been recently suggested to deflect the dangerous body, such as laser beams, microwave devices, solar panels....All these hypothesis have already been formulated but need much more time to be realized.
An interesting idea could be to use solar panels planted on the asteroid surface to use the Sun radiation as energy to move the asteroid off course.

Another interesting possibility that deserves some attention, is the use of NEOs as future resources, studying possible exploitations of these threatening objects.