Well, I don't know, I hope you will agree with me, that for this happening in the past, particularly if it leads to such wonderful things as humans was quite all right; but for us to be subject to extermination as the dinosaurs have been, that is a less wonderful prospect. Of course, who cares about it? It will take 100 million years before it happens. It might happen, it's a small probability, sooner. And here is the very remarkable thing. This rare catastrophe, an immense catastrophe, will practically certainly be predictable by careful observation and probably preventable. We may find ways, I'm sure we will find ways, either to break up or slightly to deflect such big objects and a slight deflection is abs- suffice to cause such an object to change its orbit from one hitting the Earth to one avoiding the Earth, at least by a few Earth radii. I believe that early attempts to accomplish this could be performed by careful observation, careful calculation, and impact of the object- on the object from fast- by fast, relatively small missiles shot up from the Earth. In the end for the bigger object it is apt to be true that the deflection will require the energy carried in a nuclear explosive. That might be the only way to do it for the big objects and it might be in any case the least expensive. But initially we don't need to talk about it. What is apt to happen in the next few thousand years, that is, that may happen with a probability of one-tenth of a percent or 1% even, in the life time of those who listen to my talk, these smaller objects probably can be dissuaded from hitting the earth, or else broken up and thus not producing any harmful effect. That probably can be done with the expenditure of $100 million worldwide or less; the preparation not much more than a few years.