2023-02 Results of a new asteroid surface survey.

The NEOROCKS project: surface properties of small near-Earth asteroids

Source (ArXiv)

This paper reports new initial spectroscopic analyses of the surfaces of 42 asteroids. The main result for space enthusiasts is that there is not one "M" class asteroid (metal-rich) surface in the collection.

The imagery that (many) people grow up with from Hollywood and TV "science" "documentaries" is that the Solar system is full of asteroids which are made of metal ready for mining to produce solid ingots of precious metals, with which the metals markets of Earth are likely to be crashed. That's Hollywood (perhaps somewhat influenced by a number of PR companies indulging in metals market manipulation), not reality. This result is about what you'd expect from the proportion of metallic asteroids - about 0.5%.

Some other pointers : Nearly 40% of the observed NEOs (16 out of 42) are classified as PHAs. PHAs are Potentially Hazardous Asteroids. It's not terribly surprising - all asteroid surveys are going to be biased towards the bright ones - which means those that get relatively close to Earth (well … until we have significant observatory capability at (say) Earth-Sun L2 and L3). It sounds a frightening statistic, but it's not something that's going to keep me awake at night.

The asteroid mining fraternity dream of taking apart an M-type asteroid like Psyche, which is fair enough as a dream. But they are relatively rare asteroids. Realistic "ISRU" (In-Situ Resource Utilisation) plans are going to have to expect to digest around 200 silicate mineral (and clay ("phyllosilicate"), and ice) asteroids for every metallic one they digest.

I suppose I should mention that 9 of the 42 bodies fall into the broader "X" classification, which can contain "M" class asteroids with less distinctive spectroscopic results - such as asteroids with only a small amount of metal on the surface. Given the size of the set considered in this work, up to one quarter of one of the bodies observed might be metallic. Which is still not terribly good news for the asteroid miners. In reality, almost all asteroid mining is going to find (and need to use) is silicates, and probably a fair amount of "ices" which could feed a "plastics" processsing plant. If you have inherited a vision from SF of massive foundries smelting whole asteroids into "hull metal", best leave that image in Hollywood.

The NEORocks program's home page is here. One of their main aims is to focus on extremely high standards in data dissemination, and I hope this helps them.

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This went up onto Slashdot at https://science.slashdot.org/story/23/03/18/0341259/small-near-earth-asteroid-surfaces-have-few-precious-metals-study-finds, but the editor ("EditorDavid") stressed the "precious metals" aspect of it, which I never considered in the least bit important. Ho hum - have to be more careful about writing things that @EditorDavid is likely to re-write.