The comets and asteroids that are potentially the most hazardous because they can
closely approach the Earth are also the objects that could be most easily exploited for
their raw materials. It is not presently cost effective to mine these minerals and then
bring them back to Earth. However, these raw materials could be used in developing the
space structures and in generating the rocket fuel that will be required to explore and
colonize our solar system in the twenty-first century. It has been estimated that the
mineral wealth resident in the belt of asteroids between the orbits of Mars and Jupiter
would be equivalent to about 100 billion dollars for every person on Earth today.
Whereas asteroids are rich in the mineral raw materials required to build structures in
space, the comets are rich resources for the water and carbon-based molecules necessary
to sustain life. In addition, an abundant supply of cometary water ice could provide
copious quantities of liquid hydrogen and oxygen, the two primary ingredients in rocket
fuel. It seems likely that in the next century when we begin to colonize the inner solar
system, the metals and minerals found on asteroids will provide the raw materials for
space structures and comets will become the watering holes and gas stations for
Reference: Lewis, John S. Mining the Sky: Untold Riches from the Asteroid, Comets, and Planets. Addison-Wesley, 1996.