A large ring of asteroids in orbit around the Sun between Mars and Jupiter. The total mass of all the asteroids together is less than the mass of the Moon, but the total area accessible for mining is much greater. In 2037 Nanobots were sent to the Asteroid Belt to start the mining effort. Asteroids were hollowed out by the nanobots and the excavated material was used to turn them into habitable complexes where people could work and live. These complexes were all connected together forming what is now called Astropolis, the largest city of the solar system. Presently almost a million people live and work in the Asteroid Belt. These Belteans, as they call themselves form a tight community even though the distances between different complexes are sometimes best described in astronomical units. The leftover materials were sent to Earth or other location where was is needed.

The largest asteroids in the Asteroid Belt were not touched by the nanobots. These asteroids are complete worlds by themselves. The largest of them, Ceres, is 932 km in diameter making it more a moon than an asteroid. It has to be decided what to do with them. Should they be mined and thus destroyed? Or should people start living on the surface? The problem with these worlds is that they are just too big for the tethersystems which create artificial gravity. At the same time they are so small that the natural gravity is almost negligible. Ceres has recently been proposed to be relocated to Mars, where it will become a Mars moon.