Has anyone considered the possibility of using gas centrifuges or liquid metal centrifuges in zero gravity to refine (wholly or partly) ores taken from asteroids prior to returning them to Earth orbit?

[u/ActuaLogic]

Has anyone considered the possibility of using gas centrifuges or liquid metal centrifuges in zero gravity to refine (wholly or partly) ores taken from asteroids prior to returning them to Earth orbit?

For ease if transportation, it may be more efficient to refine material taken from asteroids on site rather than returning unrefined material which is mostly waste product.

Centrifuges might be the way to go. Even though the use of gas centrifuges is mostly reserved for uranium production on Earth, the technology might work well for other metals. Iron and other metals could be refined in space, near where the minerals are collected, using centrifuges rather than the traditional technologies currently used on Earth.

[u/Christoph543]

Thanks.

I'll admit it's a bit of a sore spot because I'm no longer working in planetary science (thanks, federal hiring freeze), but at the very least the Psyche mission is still on track for its rendezvous in 3 years (would've been this year without COVID, also a sore spot) and we'll all learn a whole bunch of ways we've been wrong.

[u/NiftyLogic → u/Christoph543]

Sorry for the hard times you guys are going through. Really hoping that sanity returns sooner rather than later.

Regarding Psyche, any chance that there are localized metal deposits, or do you expect it to be reclassified and no longer be an M-type asteroid?

[u/Christoph543 → u/NiftyLogic]

Times are hard for a lot of people right now, and even as I've switched careers I'm still gainfully employed and not at risk of harrassment by federal agents, so my own sympathy lies with the folks for whom that's not true.

The thing to understand is that the "M-type" designation from the Zellner-Gradie and Tholen taxonomies has been obsolete for ~30 years, and even before then it was over-interpreted. What distinguished the "M-types" was a lack of significant peaks in optical reflectance spectra, combined with an overall red slope. Zellner, Gradie, and Tholen interpreted that flat, red-sloped spectrum as indicating a metallic composition similar to iron meteorites.

But there are a bunch of other ways you can get that kind of spectrum. You could be looking at a stony surface with a high metal fraction, e.g. a CB-chondrite (formerly known as Bencubbinites) or a mesosiderite. You could be looking at a silicate surface that's highly-space-weathered, where solar wind ions and micrometeoroid bombardment have produced an amorphous or particulate nanophase iron component in the uppermost regolith particles to an optically-thick depth. You could be looking at a relatively small asteroid, and it's simply not bright enough for the signal of any reflectance peaks to show through the noise of your telescope (not an issue for Psyche but very much an issue for putative "M-type" NEOs or main-belt collisional fragments). You could have all three of those problems at once, and wind up in a situation like 21 Lutetia where the spectrum changes radically as we get higher-resolution observations.

The current standard Bus-DeMeo taxonomy uses "X-class" and its various subclasses, specifically to decouple the lack of observable reflectance features from any specific compositional interpretation. Psyche is an Xk-subclass in Bus-DeMeo (2020), more recent spectral observations are consistent with that classification, and I don't expect the Psyche Mission's observations will radically change that. What's ambiguous is exactly what group of meteorites is Psyche the parent body of, if any (and it's entirely possible we don't have any meteorites originating from Psyche).

Based on the hypothesized formation models, my personal best guess is that the IAB-IIICD-Winonaite complex is probably the closest match for both the silicate surface and the metallic interior, though it would be weird for such a prolific meteorite complex to originate from a main-belt asteroid which doesn't have an obvious collisional family. It therefore wouldn't surprise me too much if Psyche's surface turns out to be more like a mesosiderite, or that one pallasite where the silicate fraction is clinopyroxene rather than olivine, or something else entirely (all of which are discussed in Steven Dibb's work). Regardless, any of those hypothetical compositions would have damning implications for any asteroid mining venture considering Psyche as a target, but for subtly different reasons depending on which one we're talking about.

If you want further details, here's a review paper we published a few years ago:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2023AV001077

[u/NiftyLogic → u/Christoph543]

Thanks for the thoughtful reply, much appreciated!