welshie wrote:I'm afraid no defence system would work against a rock that big! 
Putting the McLaren jokes aside, they (NASA, the ESA, the RSA etc) need to deveolp such system as if it actually happens that a big rock heads this way we will be able to save ourselves. Otherwise it will be another "Atalantis" type castropaphy (How do you spell that damm word!). Although Atalantis was submerged some 40,000 years afo for different reasons, the advanced civilisations of the time were very much wiped out and the surviving peoples had to start again. So if life as we know it survives a big rock collision, most knowlege will also be wiped out and we would have to begin again and perhaps another 40,000 years from now we will see another advanced human civilisation on Earth. To avoid this and allow us to continue at out present rate without such setbacks we need to learn now how to defend ourselves from such dangers. We have the means and technology to do so, I am sure of this. They just need come up with something and test it somehow as well. Who knows maybe they are already doing this. They have talked about it many times. Do you really thing no one is actually doing nothing about it given we know of the grave dangers that may lay ahead?