He assumed that mining operations would want to focus on iron-nickel asteroids (known as M-type), considered the most promising targets for finding so-called platinum-group metals. These include platinum, along with iridium, palladium and others.

These are rare in the Earth’s crust because they dissolve in molten iron, instead being mainly concentrated in the planet’s core. Platinum and palladium are the most economically important, having a wide range of uses in industry. But according to the analysis, just 1% of near-Earth asteroids are rich in these elements.

Suitable asteroids also need to be relatively easy to reach, further narrowing the pool by ruling out all but the nearest objects to Earth. The operative parameter here is delta-v – the change in velocity needed to send mining equipment to the target and return with a larger mass of ore.

The size of the target is also a factor; the paper suggests it wouldn’t be worth mining asteroids smaller than about 100m because the total value of the ore they would produce wouldn’t be enough to cover the costs of a space mission.

However, Dr Elvis points out that the ore values in his analysis range from a low of $800m to a high of $8.8bn.

Few asteroids are worth mining, suggests Harvard study

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