Of course Human beings have proven they can survive in rather hostile places: the moon base, the L-5 free space colonies, the Martian observation stations, and the deep space observatories on Ganymede and Titan have all existed for several centuries. Yet these outposts in our Solar system do not provide satisfactory homes for large numbers of people. The handful of scientists and technicians who occupy these bases must live within the artificial pressure of tightly closed structures, and artificial means are required to sustain their lives. Since the number of inhabitants is small, they must concentrate on specialized forms of space industry, importing virtually all consumer goods.

Human beings cannot exist indefinitely on food, water, and air alone. We require open spaces, sunlight, plants, animals, and large numbers of our fellows with whom we can trade ideas as well as objects. We can’t make any artificial environment large enough to satisfy these needs, so even the “permanent” colonies of our Solar system serve only as way stations for our expansion into space. Any large, permanent, self-sustaining Human colony needs a world similar to our Earth in many respects.