The near-Earth asteroids vary widely in composition. Each asteroid contains water, metals, and carbonaceous materials in various amounts. Some asteroids store truly vast quantities of water, while other asteroids are concentrated in metals rare on Earth.
Water from Asteroids
Water from asteroids is a key resource in space. Water can be converted to rocket propellant, or supply the needs of humans living off Earth, and can completely change the way we explore space with rockets. A single water-rich 500-meter-wide asteroid contains 80 times more water than the largest supertanker could carry and could provide, if the water were converted to rocket propellant, more than 200 times the rocket fuel required to launch all the rockets ever launched in human history.
Rare Metals from Asteroids
Once we are able to access, process, and utilize asteroid water resources, mining metals becomes more feasible. Some near-Earth asteroids contain platinum group metals in much higher concentrations than the richest Earth mines. In space, a single platinum-rich 500 meter wide asteroid contains about 174 times the yearly world output of platinum, and 1.5 times the known world-reserves of platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum). This amount is enough to fill a basketball court to four times the height of the rim. By contrast, all of the platinum group metals mined to date in history would not reach waist-high on that same basketball court.
Other Asteroid Resources
Asteroids also contain more common metallic elements such as iron, nickel, and cobalt, sometimes in incredible quantities. In addition to water, other volatiles, such as nitrogen, CO, CO2, and methane, exist in quantities sufficient to warrant extraction and utilization.