Mining Asteroids

With a diameter of roughly 250 kilometres and a mean distance from the Sun of about 2.9 AU, 16 Psyche is one of the larger main-belt asteroids, which in itself isn't out of the ordinary. However, spectroscopic studies indicate that it is made almost entirely of metal. A lump of metal 250 km across. It sounds almost too good to be true, yet we are also fortunate enough to have samples of these types of asteroids right here on Earth in the form of meteorites. This evidence has allowed scientists to put together a theory on how bodies of such seemingly unusual compositions were able to form in the first place.

Differentiation

The process of differentiation occurred in the early history of the solar system whereby primitive bodies grew large enough for melting to occur. The metals (such as iron) became physically segregated and sank to form a core, while the lighter materials floated and cooled to form a crust. Further impacts with other bodies caused fragmentation, sometimes to the extent where solid chunks of the core or crust were separated from the parent body. This explains the differing compositions of the observed asteroid/meteorite populations: some metal-rich, others metal-depleted depending on which part of the parent body they originated from. In addition, undifferentiated asteroids are also found, largely unchanged from their primordial composition.

Asteroids are grouped into several compositional classes according to their spectroscopic properties, the most notable of which are summarised in the table below.

Principle Asteroid Types

Type	Composition
M	Metal
E	Silicate rocks
S	Stony-iron
C	Carbonaceous
P	Carbonaceous/volatile
D	Frozen volatiles

However, while big type M (metal-rich) main-belt asteroids would seem the obvious choice for future prospectors, it's likely that the initial mining expeditions would focus on Near-Earth Asteroids with compositions closer to type S. One reason (as well as accessibility) is that it would be easier to set up a mining operation on an asteroid with at least some indigenous water content (to support human life and to use as rocket fuel). Also, M and E type asteroids are rarer than than types S and C. (Types P and D are not found in the near-Earth population as they would evaporate in a short space of time. Indeed, if they were to enter near-Earth space we would observe them as comets.)

To give you an idea of the potential market waiting out there, it has been estimated that a typical type S (stony) asteroid, 1km in diameter, would be worth $150 billion for its platinum group metals alone. And this is before considering the other, more abundant high grade metals that could be mined, such as iron, nickel and cobalt. One way of extracting these metals could be to combine them with carbon monoxide to form liquid carbonyls, from which the pure metals can be easily separated later on.

Mining asteroids won't be straightforward, but as the human presence in space expands beyond Low Earth Orbit, prices like $150 billion will be hard to ignore...

The logical successor to NEAR Shoemaker's detailed study of Eros would be a multiple-asteroid survey, enabling the data to be put into its proper context. Indeed, the coming decades could see a wave of "asteroid prospecting" missions, investigating NEAs not just for their scientific properties, but also for their commercial potential.

If you want more information, permanent.com contains a lengthy and detailed discussion on the logistics of future asteroid mining operations. For further details about NEAP and other planned commercial projects, have a look at SpaceDev's site.

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