11.           Countermeasures 

Studies have been conducted in both the United States and Russia on methods of avoiding potential NEO impacts. There are three possible courses of action available once a threat has been identified:

11-1.     Destruction   

The possibility of destroying potential impactors, probably with high yield nuclear weapons, has been studied in some detail. With the current lack of detailed knowledge of the exact composition of particular objects, and their structural strength, there is an element of doubt as to the effectiveness of this course of action. The fear would be that incomplete disruption of the object would subject the Earth to multiple impacts from pieces of the original body. The effects of transforming a cannon ball into a cluster bomb could be more far-reaching than the original threat.

11-2.     Deflection / Acceleration / Deceleration      

Assuming that a potential impactor can be identified early enough, its orbit could be modified sufficiently to ensure that an impact would not occur. The amount of modification required is inversely proportional to the time available before impact, so early warning of a potential threat will be crucial. Methods considered include the detonation of a nuclear weapon close to the body to change its orbit or the use of propulsion units or mass drivers (using the material of the object itself as fuel) to physically drive it from its path. Only very small adjustments would be required to ensure a miss rather than a hit.

11-3.     Evacuate/Ride the Storm 

Given enough warning, and an accurate ground-zero prediction (both entirely feasible), it might be possible to evacuate the point of impact and areas in danger such as low-lying coastal regions.  This might be an adequate course of action for small impacts (with local or regional effects), but for larger, globally threatening events, long term protection and supply will be necessary for any surviving population.  Natural food sources will not be available for over a year, and even then, there will be no infrastructure to support society once the skies have cleared.  Major climatic changes resulting from the effects of the impact may make the environment hostile to human survival for extended periods, making the re-establishment of civilisation problematic.  It might be a case of “out of the frying pan, into the fire”.