Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets, is a 1997 book by University of Arizona Planetary Sciences professor emeritus John S. Lewis that describes possible routes for accessing extraterrestrial resources, either for use on Earth or for enabling space colonization.

For instance, Chapter 5 ("Asteroids and Comets in our Backyard") exhaustively catalogs the types of near-Earth objects (asteroids and extinct comets whose orbits intersect Earth's), assessing both the harms likely from possible collisions with Earth (the subject of Prof. Lewis's previous book, Rain of Iron and Ice) on the one hand, and their potential for profitable exploitation on the other.

[2] To illustrate this potential, Lewis includes an order-of-magnitude estimate of the economic value of the smallest known metallic (M-type) near-Earth asteroid: 3554 Amun.

They merely serve to suggest that the economic benefits of obtaining such enormous resources would probably far exceed the costs involved in accessing them.)

[1]: 255  He claims that colonies built with the natural resources of the asteroid belt alone, including limitless space-based solar power, could eventually support a vast civilization of "several tens of quadrillion (1016)s of people".