How badly do you want to eat?

Mike, in the comments to my last post:

Sound like if we get desperate enough, asteroid mining may be coming sooner rather than later.

And I'm too much of a nerd not to rise to that bait.

A quick bit of searching on mining asteroids specifically for Indium and Gallium turns up this PDF from 2001, which gives us some numbers to play with. Basically, if you'll turn your hymnal to page 7 you'll see that concentrations of Indium and Gallium are so small in asteroids (as they are on Earth) that mining a gigatonne-sized asteroid for metals in concentrations of a few parts per million is a lot of work. That said, the vast majority of the mass of a metallic asteroid is Iron and Nickel which can both be separated out easily, so it's conceivable that an asteroid mine would reduce the mass returned to Earth by shipping undifferentiated metals that have been separated from the nickel-iron dross. Still, I've got to believe that there would be other options, like for example giving up our precious LCDs.

Ah, but something else caught my eyes (it always does, I'm terrible in libraries.) Gallium is present (on average) in concentration of 60 ppm, Indium only 0.46 ppm. But Phosphorus is present, on average, in concentrations of 1600 ppm. Still not a lot, but that depends on your perspective. If agriculture starts to stagnate or collapse because of dwindling phosphorus reserves our attitudes towards what's "affordable" and not might change, and quick. On a planet of 9 billion people, phosphorus will be non-negotiable.

Problem: the paper posits a mine capacity of 10 kilotonnes of phosphorus per year, while world demand is more than 100 megatonnes. So we'd need something like 10,000 mines to satisfy world demand. Still, back in the days of Guano Imperialism (god I love that phrase) Britain sent warships to Peru to guard the, uh, stuff. There's more than enough asteroids to satisfy that kind of demand, it's just a matter of expense.

As a side benefit to producing life-giving phosphorus, the mines would also be producing oodles of platinum, gold, silver, and of course indium and gallium. So in this model, a crucial food production infrastructure would also subsidize our giant flat-screen habits. And, on top of everything else, the Earth's phosphorus may have come from space in the first place. That's space exploitation I can get behind!

Update: I've officially put too much thought in to this, but the above discussion is all based on numbers from M (metal-rich) asteroids. C (carbonaceous) and S (stony-iron) asteroids are much richer in phosphorus. S are interesting candidates for mining because they also have useful metals like silicon, aluminum, and useful chemicals like water, carbon, and sulphur.