Popular media loves to talk about asteroid mining with big numbers. Many articles talk about a mission to Psyche, the largest metallic asteroid in the asteroid belt, as visiting a body worth 1000000000000000000000000, presumably because their authors like to press the “0” key on their keyboards. But how realistic is this assessment? And what does it actually mean? A paper funded by Astroforge, an asteroid mining startup based in Huntington Beach, and written by a professor at the Colorado School of Mine's Space Resources Program, examines in detail what metals are available on asteroids and whether they are actually the case is worth as much as the simple calculations suggest.
The paper divides metals on asteroids into two different types – those that would be worth returning to Earth and those that would not. In fact, the only metals worthy of a return to Earth are the platinum group metals (PGM), known for their exceptionally high cost, relatively low supply, and high utility in a variety of modern technologies. This also includes catalytic converters, which is why they are often the target of thieves.
The other category would be metals used for construction in space, such as iron, aluminum and magnesium. Although their relatively low prices on our home planet make it economically unwise to send them back to Earth, they are useful in space for building large structures such as space stations or solar arrays. Given the chicken-and-egg problem of no demand for these space-derived metals because they are so expensive, it is difficult to quantify their value. However, competition (e.g. launching the material from Earth) is affordable, costing $10,000 per kilogram, plus $100 per kilogram for a common material like iron.
Fraser talks about whether we would mine asteroids.
While these prices are nowhere near the $500,000 per kilogram that a PGM like rhodium ever commands on Earth, it could still make iron mining on asteroids economically viable if the material is used in space. What do all of these calculations mean for the actual value of the asteroids we could mine?
First and most importantly, recent research suggests that “pure metal” asteroids, as Psyche is believed, are likely pure fiction. While that may not be good news for a single harmless asteroid that's worth a lot, the other part of this research is that even asteroids originally thought to have relatively low metal content actually have reasonable amounts, that could be economically supported.
To prove this, the paper examined in detail a series of meteorite studies, which represent the equivalent of leftover asteroids, and compared the “contents” of 83 different elements with ores found on or near Earth's surface. Because remote sensing makes it difficult to distinguish between some of these elements, meteorite samples that can be subjected to advanced analytical techniques are our best bet for accurately calculating the chemical composition of asteroids, aside from the few samples of intact asteroids obtained in this way were returned far.
Isaac Arthur also discusses the prospects of asteroid mining.
Image Credit – Isaac Arthur YouTube Channel
These data showed that although the concentration of PGM is lower than originally thought (based on an assumption made in a fundamental paper on the composition of asteroids), it is still present in much higher concentrations than the corresponding terrestrial ores. In particular, a material known as a refractory metal nugget (RMN) could have PGM concentrations orders of magnitude higher than anything found on Earth or other types of asteroid material.
RMNs are mainly found in a calcium-aluminum inclusion structure (CAI), mainly on L-type asteroids. L-types are relatively rare asteroids with a reddish color, but we have not yet visited them. However, they could consist of more than 30% CAIs, in which case they could contain a significant amount of extractable PGMs without additional processing.
However, RMNs themselves are very small, in the micrometer to submicrometer range, which makes them extremely difficult to process in the first place. Therefore, mass extraction from asteroid regolith could be up to hundreds of ppm, which is already several orders of magnitude higher than their concentration in Earth's regolith.
Fraser talks about mining Psyche, the largest “metallic asteroid” in the asteroid belt.
Looking at the metals for use in space, they are about as abundant as originally predicted, but they are difficult to process from their oxidized state. Typically this requires a high-energy process, such as electrolysis of molten regolith, to break out the elemental metal needed for further processing. Again, the chicken-and-egg problem is having a power source large enough to perform these processes, but building it would require the material the power source would require.
Eventually this problem will go away as companies like AstroForge get their way. Remember that the company funded this study and that its two co-founders and Kevin Cannon, the professor at CSM, were co-authors. The company plans to launch its next mission in January, a rendezvous with near-Earth asteroids to find out if they are “metallic.” Perhaps this mission will contribute to our growing understanding of the composition and value of the asteroids around us.
Learn more:
Cannon, Gialich, Acaine – precious and structural metals on asteroids
UT – What are asteroids made of?
UT – What is the difference between asteroids and meteorites?
UT – Asteroids: 10 interesting facts about these space rocks
Mission statement:
Asteroid mining concept.
Photo credit: NASA/Denise Watt
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