The asteroids or, more properly, the minor planets, have long been suggested as possible sites for human colonization. The idea is popular in science fiction.
Digging the colony under meters of asteroidal rock would give protection from cosmic radiation.
Asteroid mining, a proposed industrial process in which asteroids are mined for valuable materials, especially platinum group metals from metallic objects, may be automated or require a crew to remain at any target.
- Large number of possible sites, with over 300,000 asteroids identified to date
- The large numbers mean lots of places to colonize, see also the anti-congestion argument.
- Asteroids contain several chemical composition classes, including iron and carbonaceous, providing a variety of materials usable in building and fueling spacecraft and space habitats. The Trojan asteroids, in Jupiter's orbit may be primarily extinct comets.
- Some Earth-crossing asteroids require less energy (delta-V) to reach from Earth than the Moon.
- Material mined from asteroids could be a basis for a trade economy.
- Many asteroids (especially the extinct comet cores) contain large amounts (more than 5% of total composition) of volatiles and carbon, which are necessary for life support.
- Isaac Asimov pointed out the advantage of building cities inside hollowed out asteroids (see hollow asteroid/comet colonies) since the interior area in square miles of all the asteroids put together is a great deal more than that of the surface area of Earth (viewed as a series of cubes one mile (1.6 km) by one mile resting on the surface of Earth) and thus a large population could be accommodated in the asteroid belt.
- Low gravity. Humans would have to adapt, or asteroids would need to be given a sufficient spin to induce artificial gravity. See also manipulated spacetimes (section weakly manipulated spacetimes). It is arguable that the gravity issue is no more a problem than the fact that light-skinned Humans would have difficulties "returning" to Humanitys ancestral home Africa due to ultraviolet radiation. After all, why should Earth have such a central position in a cosmic human culture, except from the fact that Humans originally evolved there? Another solution is artificial gravity colonies.
- Most asteroids are far from the Sun. The main asteroid belt is roughly 2 to 4 times further from the Sun than Earth. This means that the available solar energy (solar constant) is 4 to 16 times less, although building large reflectors to collect sunlight is possible in space and less sunlight is in large part compensated by the lack of atmosphere, and even on Earth temperate plants live with much less sunlight than equatorial plants.
- Many asteroids may merely be loose agglomerations of dust and rocks, which may be very difficult to use.
Asteroids of special interest
- (6178) 1986 DA is a potentially metallic near-Earth asteroid.
- 216 Kleopatra is a metallic main-belt asteroid.
- 4 Vesta is the second largest object in the Asteroid Belt, after Ceres.
Some C-type asteroids are likely carbonaceous chondrites, which are some tens of percent water by mass.