If we want to colonize space, we have to figure out how to generate a large supply of life sustaining resources. The most important being water. The good news is, traces of water have been detected throughout our solar system. And asteroids may hold the most accessible abundance of water that we know of. There are likely millions of asteroids within our solar system and over 18,000 are classified as near-Earth objects - meaning they’re located relatively close to our planet. It’s estimated that collectively these asteroids could hold two trillion metric tons of water. While others are thought to hold rare Earth minerals and metals worth trillions of dollars.
There’s a lot of different types of asteroids, all of which orbit the Sun with most inhabiting the region between Mars and Jupiter known as the asteroid belt. One way they’re classified is by spectral type, which is based on their emission spectrum, color and albedo. Most asteroids fall into three classes: C-Type, S-Type and M-type each of which could be extremely valuable for their unique resources.
C-type asteroids are thought to be most common. C stands for carbon, which accounts for their dark color and a large part of their composition along with silicate rocks and clay. Meanwhile, less common, S-Type or silicaceous asteroids are greenish to reddish and are thought to be made of silicate materials and nickel-iron. Similarly, M-Type asteroids also seem to be made up of mostly nickel-iron, which is why they’re called metallic asteroids. S and M-Types are thought to be instant money makers due to their abundance of precious metals. It’s estimated a football field sized asteroid could hold $25 to $50 billion worth of platinum alone. But of all the asteroids, C-Types are referred to as the best all-around for mining and that’s because they have high abundances of water bound up as hydrated clay minerals. Water is not only critical for space colonization, but it can also be broken down into its constituents - hydrogen and oxygen - and used as rocket fuel. It takes a lot of energy to leave Earth’s atmosphere so mined asteroids could potentially solve propulsion problems by providing space sourced fuel.