Asteroids: Composition

Asteroids are unlike any mineral deposit on Earth because they are the undisturbed remains from the creation of the solar system. This leaves them relatively pristine and undisturbed in compositions that could have only formed and cooled in the microgravity of space, outside of a planet’s gravitational pull.

As the planets formed, these smaller elements continued to orbit the Sun independently. However, since the building blocks of the solar system were all of similar origin, asteroids had the same starting point as the materials that make up the Earth – just in different concentrations.

Asteroid composition can be generally grouped into three main categories – C-type, S-type, and M-type.

C-type asteroids are carbonaceous, and represent the majority of known asteroids. While not large sources of metal, they do tend to contain water (aka hydrated minerals), an incredibly valuable resource for in-space fuel. C-type asteroids are quite dark, making them harder to identify with basic ground-based observations – which means they may be even more abundant than current estimates. C-type are the most attractive targets for initial exploration by Planetary Resources, as in-space water could be the source of the energy needed to unlock more complex asteroid resources.

S-type asteroids are ‘stony’ asteroids, and tend to be composed primarily of magnesium-silicate. They tend to be quite bright and easy to identify, and are the second most frequently occurring asteroid, after C-type. While less likely to contain hydrated minerals, silicates represent a potential source of building material and radiation protection for commercial and government space operations.

M-type asteroids are ‘metal rich’ assets (sometimes referred to as X-group) and they tend to contain very large quantities of refinery-grade nickel and iron. They are less common than carbonaceous or stony asteroids, but are of long-term interest to Planetary Resources and our partners as we move into the second-wave of extraction, enabling space-based projects where metallic resources are critical.