We have many options. The National Space Society, whose more than 12,000 members are committed to establishing settlements in space, suggests that we’ll probably first go to a planet that has the resources to support life. After completing a $200-million study in 2000, NASA reported that a colony could be dug several feet beneath our own moon’s surface or covered within an existing crater to protect residents from the constant bombardment of high-energy cosmic radiation, which can damage our DNA and lead to cancer. The NASA study envisions an onsite nuclear power plant, solar panel arrays, and various methods for extracting carbon, silicon, aluminum and other useful materials from the lunar surface. The National Space Society, in its own 2008 report “Roadmap to Space Settlement,” also identifies the moon as the logical initial stop, citing the presence of life-sustaining ice there as a precursor to permanent lunar bases, hotels and even casinos.
Other space-settlement advocates suggest skipping the moon entirely. Although our moon is closer and we’ve already landed people there, the moons of Jupiter, Saturn, Uranus and Neptune are believed to contain variously greater quantities of water, carbon or nitrogen. But the most Earth-like of the destinations in our solar system is Mars. “Mars compares to the moon as North America compared to Greenland in the previous age of maritime exploration,” says Robert Zubrin, the head of the Mars Society, a group pushing for expeditions to and settlement of the Red Planet. Unlike the moon, Mars has a bit of an atmosphere, which would offer some protection from cosmic rays, and about 40 percent of Earth’s gravity.
In 2002, NASA’s Mars Odyssey spacecraft detected continent-size regions of water ice in the Martian ground, and in 2008, photographs from the Phoenix Mars lander confirmed the presence of ice there. Enough carbon also resides in the soil to grow plants, and the daytime temperatures occasionally reach a balmy 70°F. It’s plausible, too, that over time the planet could be “terraformed,” using water from underground ice (or importing it from an ice asteroid) to form a thin ocean and, much later, to create an atmosphere offering breathable air and a better shield against cosmic radiation. “It’s much easier to settle a planet than to build one,” Zubrin says. “Christopher Columbus sailed across the ocean in a boat. Imagine if he’d had to build the American continent once he got there.”
All of these suggested routes, however, may fall under the category of what Isaac Asimov once called “planetary chauvinism.” We could just as well build an orbital habitat, erecting our future home in the void and engineering each of its details to our own exacting specifications. Financially, if not technologically, it is impossible to launch the amount of materials from Earth that one would need to build a large orbiting structure. But such a habitat could be constructed primarily of resources extracted from near-Earth asteroids, which in themselves provide more terrestrial variety and potential surface area than all the planets in our solar system put together. In 1974, Princeton University physicist Gerard O’Neill presented a design of a massive freestanding orbital habitat consisting of large cylinders spinning along an axis at a rate of about one rotation per minute—just fast enough to simulate gravity along its inner surfaces—and linked to another cylinder spinning in the opposite direction to eliminate torque. In gravity-free outer space, the habitats could remain structurally sound even at sizes large enough to house thousands, or millions, of residents, and O’Neill imagined twin cylinders 20 miles in length and with an interior surface area of 500 square miles.
Al Globus, a contractor at NASA’s Ames Research Center who maintains a well-regarded space-settlement website, speaks of the O’Neill Cylinder as one would a tony gated community, a place with constant sunlight, tremendous views, spacious quarters, and dedicated areas near the axes of the cylinders for zero-G recreation. Populations on these ships would be kept well above 150 people to avoid the consequences of inbreeding, although ideally the rotating habitats would exist in socially interactive clusters. Residents could also use stored DNA whenever the gene pool needed more variety.
A primary advantage of an orbital habitat is that it would not necessarily need to stay in orbit. If a ship exhausted the resources of a nearby asteroid or had to escape a dying sun, it could be rigged up with an onboard nuclear reactor or a solar sail and sent out to any number of faraway destinations. None of the 500 planets known to orbit stars outside our solar system is believed to have an atmosphere capable of sustaining human life, but almost all of these were discovered in the past decade, leading two astronomers to conclude in a recent paper that the probability of finding an exoplanet with a habitat nearly identical to that of the Earth’s by 2264 is 95 percent. In September, a group of astronomers with the Lick-Carnegie Extrasolar Planet Survey, sponsored by NASA and the National Science Foundation, announced the discovery of a planet about 20 light-years away, in the constellation Libra, that orbits its star well within the “habitable zone” of our own orbit.
For successive generations living aboard an enclosed ship, it may not even matter if they remain in Earth’s orbit or travel for hundreds of years toward one of these extrasolar planets. They may simply float through space in their “generation ship,” harvesting materials from asteroids and comets along the way.single page