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Could we prevent the collision of a Near Earth Objects with the Earth?
The answer to this question is yes. For most Near Earth Objects we could prevent an impact by either deflecting or breaking up an object. Of these the first method is the best since the NEO does not collide with the Earth and causes no damage at all. If we choose to break up a NEO some fragments will probably still collide with Earth and cause damage. Breaking up a NEO would, therefore, be used only as a last resort.
Scientists have suggested many ways in which the orbit of even a billion tonne NEO could be changed so that it missed the Earth including attaching solar sails or engines to the object and the use of chemical or nuclear explosives. It is much easier to change the course of an object in the low gravity of space than on Earth and a NEO would only have to be moved by just over 6700 km, the radius of the Earth, in order to prevent a collision.
How easily the orbit of a Near Earth Object could be changed will depend on how long we have to overt a collision. Identifying which NEOs are hazardous is, therefore, an important part in overting impacts. With asteroids we can predict whether they will collide with the Earth many hundreds of years in advance. With comets, however, we may have much less warning. To date the orbits of around 500 Near Earth Asteroids larger than 1 km have been identified out of an estimated total of 1000.
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