The Space Review has a thought-provoking article by Stephen Ashcroft titled “What Future for Intelligent Life in Space“, which reignites the seemingly-forgotten “great idea” of the 70s: human colonisation of space. Ashcroft begins by pointing out that are a “highly inefficient means” of providing gravity and an atmosphere for human life, because “almost all the mass of the planet serves no function, from the point of view of its surface life, other than to provide surface gravity, and in some cases also a magnetic field and geothermal heat… Planets are low-tech, compressive structures.” He goes on to conclude that…
…while a planet is a good place for life to get started using unconscious means that can evolve spontaneously from the chemical substrate, once life has reached the stage of industrial development, its further growth depends on the use of technology to construct artificial space colonies, which use the material resources of planetary systems at a much higher level of efficiency.
Since, in the O’Neill colony design, about 86 percent of the mass consists of passive radiation shielding, this conclusion is not strongly dependent on the precise proportions of rocks, metals, and volatiles available. Clearly, if adequate protection from cosmic rays can one day be achieved by the use of magnetic fields, the balance swings even further in favor of designed habitats as opposed to natural ones.
In this way, very large future human populations are conceivable. For example, John S. Lewis has reckoned that the material resources of the main asteroid belt, together with large-scale use of solar power, would allow at least 10 million billion people to support themselves (Mining the Sky, p.196). When one adds in the Jupiter trojans and the opportunities presented by the outer solar system, even larger populations become possible. Frank Drake and Dava Sobel have put the overall carrying capacity of our system at “more than a hundred billion billion human beings” (Is Anyone Out There?, p.128), while Marshall Savage suggests an even larger figure (The Millennial Project, p.303). We do not need to quibble over orders of magnitude in order to make the point that the propensity for economic and population growth characteristic of industrial civilization is well matched with the opportunities offered by its local environment, provided that the 21st century sees a shift of the focus of industrial and population growth away from Earth and onto large-scale development of the natural resources of near-Earth space.
The article then uses the idea of colonisation of the solar system as a necessary stepping stone to the first inter-stellar travel by human beings. All in all, a truly fascinating article – go check it out.