Alpha Centauri's Universe: Monthly Publication

Certainly it is not to relieve population pressure on Earth. The humans left behind can surely increase in numbers faster than they can be exported. Another reason, increasingly popular today, concerns Earth's vulnerability to asteroid or cometary collision. Such an impact apparently killed off the dinosaurs 65 million years ago. Could not another one, tomorrow, do the same thing to humans? The late Eugene Shoemaker is best known as the codiscoverer of the Shoemaker-Levy comet, but he was also a recognized expert on solar system collision frequency. He estimated that an impact such as the one that eliminated the dinosaurs might be expected every hundred million years. The effects on humanity would of course be devastating, but it is unlikely that we would be wiped out. We would have every right to feel unlucky if such an infrequent event were to happen in the next few thousand years, and it seems a poor justification for a crash project to terraform Mars.

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