Moon Has More Metal Which is More Exposed in Larger and Deeper Craters

Team members of the Miniature Radio Frequency (Mini-RF) instrument on NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft found new evidence that the Moon’s subsurface might be richer in metals, like iron and titanium, than researchers thought.

Using Mini-RF, the researchers sought to measure an electrical property within lunar soil piled on crater floors in the Moon’s northern hemisphere. This electrical property is known as the dielectric constant, a number that compares the relative abilities of a material and the vacuum of space to transmit electric fields, and could help locate ice lurking in the crater shadows. The team, however, noticed this property increasing with crater size.

For craters approximately 1 to 3 miles (2 to 5 kilometers) wide, the dielectric constant of the material steadily increased as the craters grew larger, but for craters 3 to 12 miles (5 to 20 kilometers) wide, the property remained constant.

“It was a surprising relationship that we had no reason to believe would exist,” said Essam Heggy, coinvestigator of the Mini-RF experiments from the University of Southern California in Los Angeles and lead author of the published paper.

Discovery of this pattern opened a door to a new possibility. Because meteors that form larger craters also dig deeper into the Moon’s subsurface, the team reasoned that the increasing dielectric constant of the dust in larger craters could be the result of meteors excavating iron and titanium oxides that lie below the surface. Dielectric properties are directly linked to the concentration of these metal minerals.

If their hypothesis were true, it would mean only the first few hundred meters of the Moon’s surface is scant in iron and titanium oxides, but below the surface, there’s a steady increase to a rich and unexpected bonanza.

Written By Brian Wang,

34 thoughts on “Moon Has More Metal Which is More Exposed in Larger and Deeper Craters”

  1. Survey says: they’re convinced.

    Suffice it to say, greater accuracy is always better… But the notion investors will only come onboard with survey maps with a 1 meter resolution seems, I don’t know… SILLY! After all, oil companies will spend billions just to build exploration rigs in the North Sea only to come up dry… And the first resource extraction operations on the moon will likely be for what’s known to absolutely exist… Ice.

  2. You need enough accuracy where you can convince investors to invest a few billion to start a mining operation. What you need is a map that shows concentration of Platinum metals with accuracy to a few meters so you can land a rover to verify.

  3. I will agree to one thing: Metal can indeed vacuum-weld in space and on the Moon. But as I’ve said, that’s not corrosion, and certainly not oxidation, and it’s not relevant to Lunar soil.

    Actually, there is a form of actual corrosion that can occur in space outside of LEO – one you haven’t mentioned – hydrogen embrittlement due to bomardment by the solar wind. But that too is irrelevant to Lunar soil, and doesn’t cause metal depletion.

    As for your “end result is still the same”, please define exactly what “end result” you are talking about.

  4. Have you even bothered reading what I wrote, and trying to understand any of it (all 3 parts, not just the last one)? I’ve listed exactly which effects there are, and addressed each of them, including the ones in your link. Most of them are irrelevant to Lunar soil for the reasons I’ve stated. And none of them explain the sort of “metal depletion” that Brett asked about in the root of this thread. None of that is spin.

    You haven’t presented any specific effects or factors that I haven’t addressed. But you are welcome to present more effects if you think there is something I haven’t covered. I’ll happily address them.

    Btw, specifically re Brett’s original question – it stemmed apparently from a misunderstanding of the original article’s claims. The original article isn’t talking about pure metals, only metal oxides (initially, I was confused by that too). They are only claiming that the deeper regions are richer in heavy metal oxides. The shallower regions seem to be richer in silica and oxides of lighter metals.

  5. You don’t need oxygen for corrosion… Other factors, which I’ve already stated, can cause a similar corrosive effects in space (and on the Moon) as oxidation on Earth.

    Anything you say beyond this point is just spin, so you can feel as if you’re still right. The best thing to do is just admit, “Well, yeah, I guess metal could corrode in space or the Moon. It’s not classic oxidation as we see on Earth, but the end result is still the same.”

  6. (part 3)

    Now back to the Moon –

    As I said, nearly no atomic oxygen (so no oxidation), any lost electrons will be quickly replaced, and we’re not dealing with polymers or mechanical parts, so broken bonds and cold welding aren’t an issue. The original article talks about oxides, not even pure metals. (edit: We’re not dealing with electronics here, either.)

    There’ll be hardly any loss of material. If anything, it should be easier to rip out an oxygen than a heavy metal atom (the bond is the same – it’s the same oxide). And incoming protons mean a reducing environment:

    I can explain the chemistry of that in more detail, if you want.

  7. (part 2)

    A few more things before reading your link:
    – Particle radiation can also rip out atoms. But that should depend on the atomic mass and bond strength. It should be harder to rip out heavy metal atoms held by strong ionic bonds (such as in Lunar soil oxides).
    – Particle radiation can also shift atoms inside a material, or transmute them to other isotopes – causing either physical defects or chemical change.
    – Even without loss of material, physical defects and chemical changes affect the material properties, often resulting in loss of strength, conductivity, etc.

    As for your link, the 1st half talks specifically about oxidation with atomic oxygen in LEO. The 2nd half clearly states that that’s not an issue beyond 700 km or so from Earth. Mind you, the Moon is roughly 400000 km away.

    Next, it mentions cold welding, which I admit I forgot about. But that isn’t exactly “corrosion” in the usual sense. There’s no loss of material, nor even electrons, no atomic defects or chemical change. It’s just sticking two parts together. But it does cause mechanical problems by preventing motion.

    Finally it briefly mentions loss of electrons by radiation. See my notes on that earlier. I think they mostly mean broken bonds in polymers. Metals and ceramics are much more resistant to radiation damage.

    (edit: Moving atoms around in electronics is also an issue, because the working parts are so tiny. And charge buildup can damage the delicate circuitry.)

  8. I’ve studied chemistry and material engineering, I know what corrosion is. But I have no idea what you mean by “oxidizing effect“, if you don’t explain what you mean by “effect”. So I could only refer to actual oxidation. You wrote “the end result is the same”, so it seemed close enough.

    Oxidation is the removal of electrons, usually transferring them to an electronegative atom or chemical group that can hold on to them, such as an oxygen, sulfur, chlorine, etc. That usually produces a new compound, such as an oxide. In some cases, the compound dissolves in water or crumbles away, resulting in loss of material.

    Is the removal of electrons what you meant by “end result is the same”? Or maybe the loss of material?

    I can imagine that EM radiation can move electrons around and even rip them out (photoelectric effect etc), and vacuum can encourage loss of atoms. Oxygen near Earth certainly can form oxides. BUT:
    – Loss of atoms depends on the vapor pressure, which for metals is usually low. Let alone for ionic compounds like oxides.
    – Without something to hold the electrons, they’ll come back. If there’s a build-up of positive charge, it’ll attract nearby electrons (e.g. from the solar wind) to balance the charge. This won’t fix broken chemical bonds, but that’s not an issue for metals.
    – Oxygen drops off quickly farther from Earth.

    Now, on to reading your link to see if I got anything wrong. I’ll come back and reply after I read it.

  9. You may be confusing with LEO, where there is atomic oxygen from Earth’s atmosphere. There is none of that on the Moon (only atomic oxygen that may be there is from other oxides).

  10. It’s the opposite. Solar wind and cosmic rays are mostly protons, which have a reducing effect. Lunar soil is less oxidized than Earth.

    (And besides, the original article is talking about metal oxides, not pure metals.)

  11. Do note, I didn’t say the metal was oxidized, I said, ‘oxidizing effect.’ In other words, it’s not true oxidization, but the end result is the same… Oh, and by the way, a vacuum itself has a corrosive effect.

    Do a google search for “does metal corrode is space” and I’m sure you’ll find something that confirms the corrosive effect of the vacuum of space… along with other sources of corrosion.

  12. Eventually we are going to need to learn to extract what we need without the luxury of highly differentiated ore bodies such as only form with hydrothermal processes. Part of that will be learning to build working machinery from whatever is at hand. NOT what we would ideally like to have.

  13. I thought that was just released by the USGS recently using decades worth of data to give the most detailed geological assessment of the Moon to date.

    I’m certainly not saying we can’t get even more detailed, and thus more surveying should be performed, from both in orbit and on the surface, but you make it seems as if no one’s even taken the fruitive steps to produce what you’re talking about.

  14. Corrosion from constant bombardment from high energy, high frequency radiation would certainly have an ‘oxidizing effect’ on metal.

  15. Totally makes sense.

    If it’s comes from asteroids, of course the crater will have an excess of metals, and if it’s natural to the Moon, an asteroid slamming into the surface would expose it.

  16. After reading the linked article, they are talking about having more iron and titanium oxides at greater depth. The surface seems to be richer in silica and other metal oxides (calcium oxide, alumina, magnesia).

    Silica dielectric constant: 3.9
    Sapphire (alumina), calcium oxide, magnesia: ~10
    Iron oxide: ~15
    Titania: ~90-170

    They’re also taking about bigger depths, up to 2 km.

    Having more vacuum fraction and more reduced oxides should reduce the dielectric constant close to the surface, but there seems to be more going on than just that. Maybe the silica dust settled later during formation, so there is some differentiation?

  17. See my reply to DrPat. I think their conclusion is upside down (at least based on the bits quoted here, without reading the original article).

  18. The top soil is mostly oxides – of metals and silicon, but the result is a mix of ceramics. There are plenty of metal compounds (oxides), but almost no free metals.

    The oxides are pretty good insulators themselves, but dielectric constant tends to be higher for better insulators, and actually vacuum has the lowest dielectric constant than (almost?) any insulator.

    They say the dielectric constant increases with depth. This means better insulators further down, not better conductors. I can think of two possible explanations:
    1. More compact soil => less vacuum fraction.
    2. Younger surface => less exposure time to solar wind and cosmic rays => more fully oxidized soil (less reduction by incoming protons).

  19. What we need to do is assay the moon. A mineral assaying satellite orbiting the moon at low altitude scanning the entire surface and mapping mineral deposits. One we have the global assay map we can send rovers to do detail assays. Platinum Metals could be profitable mined on the moon.

  20. ‘Economically extractable’ is a very relative concept.

    When arriving there costs several tens of millions USD per ton (and this if SpaceX achieves its goals), then using unlikely ore refining schemes could become reasonable again, if the locally sourced materials are competing against such prices per ton from Earth.

  21. While technically regular rocks are silicates of typically Aluminium and Magnesium, these metals are too bound up in stable crystals to be economically extractable and, indeed, to mess about with the dielectric constant of craters. What we probably have below ground are concentrations of much purer metals, like [telluric iron](, like we would have on Earth if the Oxygen hadn’t oxided the vast majority of it three billion years ago.

  22. So if the top few hundred meters of the moon has no metals, then what has it got?
    There really aren’t that many elements that are neither metals nor useful gases (such as oxygen, nitrogen etc).

    Let’s ask mr google: composition of moon

    The average composition of the lunar surface by weight is roughly 43 percent oxygen, 20 percent silicon, 19 percent magnesium, 10 percent iron, 3 percent calcium, 3 percent aluminum, 0.42 percent chromium, 0.18 percent titanium and 0.12 percent manganese.

    So, 43% oxygen. That sounds useful.
    The rest: silicon I’ll grant is non metalic.
    19% Magnesium? 10% Iron? Calcium, aluminium, chomium…
    What sort of element are these? Huh? Noble gases perhaps?

  23. But, what would deplete just the top few hundred meters of the Moon in metals? That’s a tiny, tiny depth on the scale of the Moon, and it’s not like the metals are particularly volatile; If they started out there, they should remain there.

    It’s like the whole metal rich moon got coated with a thin layer of metal poor material. Several billion years of meteoric infall? A big meteor hitting a very poor region, and spreading it about? The dinosaurs not bothering to mine below 200 meters?

  24. These are measurements of astronomical scale. We just need a small good spot to get started with ISRU. Good news, but not a game changer. Go to the Moon 40 years ago!

  25. If true, then it would seem like large craters within large craters might have dug even deeper, which could be a test on their hypothesis – and also point to possible areas to do mining.


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