Uranium found on the Moon

By Phil Plait | June 29, 2009 5:25 pm

Scientists using data from the recently-Moon-smacked Kaguya spacecraft have found evidence of radioactive elements on the lunar surface, including, for the first time, uranium!

That’s pretty cool. It’s a little unexpected to me, too. One of the key aspects of the Moon is that it’s not as dense as the Earth — in fact, it’s just a bit more than half the Earth’s density — so you don’t expect it to have a lot of denser materials. Also, dense materials tend to sink and lighter ones float in a liquid, and we know the Moon was once entirely molten. So most of the uranium (which is among the densest of all elements) should be near the Moon’s core, not on the surface.

Most, but not all. It appears there is some on the surface!

[Update: I received some comments and email (hi Emily!) about this. I was trying to simplify the story about dense stuff sinking and I suppose I left off too much; of course, since we find uranium on the Earth's surface it can't all sink down. Basically, uranium likes to bind with oxygen, and that makes it into a less dense molecule which doesn't just drop all the way down to the core, and that's why it can be found on the Earth's surface. I appreciate the comments on this -- they keep me honest and usually give me a chance to learn something.]

Uranium on the Moon

The way you detect uranium is by gamma rays (having an old prospector pan for it probably won’t get you far, even if he has a Geiger counter). The nucleus of a uranium atom is packed with protons and neutrons; Uranium-238, for example, has 92 protons and 146 neutrons all coexisting in a little ball. Because of the weird ways of the quantum mechanical world, this nucleus is unstable, and after a while it spontaneously ejects a little clump of two protons and two neutrons: a helium nucleus, or what’s called for historical reasons an alpha particle.

Along with this alpha the uranium also emits two gamma rays, photons of light with very high energy. These photons go screaming off in some random direction. In this case, enough gamma rays were sent to the then-still-orbiting Kaguya’s gamma ray detector that it was able to see them. Different elements decay in different ways, and so they send off gamma rays with different energies, too. Kaguya’s detector was built to distinguish between these different gamma rays, and that’s how the scientists knew they had found uranium.

And it’s also how they found other elements like thorium, potassium, oxygen, magnesium, silicon, calcium, titanium, and iron, too. We already knew that there was oxygen and a few of those others on the lunar surface, but this method of mapping from orbit is effective in finding these particular flavors (OK, isotopes) of the elements.

What does this mean? Practically, not a whole lot for now. It’s not like the first astronauts to go back to the Moon will get rich mining uranium, or even have enough to use it for power. In the future, however, any colonists will have to do large-scale mining to get access to aluminum, oxygen, and other things they need to build and survive on the Moon. Maybe they’ll find uranium in useful quantities then. It’s not a good reason to go back to the Moon, but it’s something for future space travelers to remember.

But what this does do is give us more clues into the birth, history, and evolution of the Moon; how it’s changed since it formed over 4 billion years ago. We’re pretty sure the Moon formed when a Mars-sized object slammed into the Earth, and the ejecta coalesced into our satellite. But we can always learn more details, and those help us understand just how this happened, and what has changed since.

More knowledge is always good. You never know where it may lead. This is another step in understanding the Moon, and one day it’ll be the home for a lot of people. The more we know, the better.

Prospector image from ToOliver2′s Flickr photostream.

CATEGORIZED UNDER: Astronomy, Space

Comments (62)

  1. Jeff

    The moon was derived in part from the earth’s crust, which has some uranium pockets in it.

    So in the weak moon’s gravity, it probably wasn’t totally differentiated into lunar core, and some remained in lunar crust. Kind of makes sense.

  2. I was half expecting to see the astronaut picture from Watchmen with Dr. Manhattan being reflected in the helmet glass. Seems appropriate.

  3. Sarah Langford

    Won’t mining the moon make building a space elevator more viable, as we need something to send down as well as up?

  4. Flip

    We must defend the moon from terrorists trying to acquire nukes!

    Going back to the moon will now be an Air Force project.

  5. Sven

    This just in: Iran is building a moon rocket “for science”. ;)

  6. Actually, you don’t expect uranium to sink to the centre of the moon, any more than it would sink to the centre of the Earth. For chemical reasons, uranium gets concentrated in the sorts of rocks that make up the crust. See, for example, this web page.

  7. Uranium is a dense element in pure form, but in natural conditions it tends to oxidize to U2O7. Since oxygen is a light element and a large ion, oxidized uranium is actually fairly low density, and tends to segregate to crustal rocks (lithophiles) rather than mantle or core rocks (siderophiles). While some of the highest concentrations of uranium are in sandstones and organic rich sediments (it has an ungodly affinity for free carbon), under non-biological conditions, it tends to segregate into granitic rocks… which is why communities over granitic bedrock are particularly at risk with respect to radon.

    Also, due to the moon’s short geological (selenological?) history, other than magmatic processes, most of the pathways that lead to elemental concentration on earth- the formation of ores- simply never had a chance to occur on the moon. I suspect that most materials that we think of as “ores” on earth will be fairly disseminated at low levels in most cases. But the solar power available is likely to render energy costs minimal, so elemental concentrates may not be as important as starting materials.

  8. Of course, the fact that the uranium is on the surface raises the possibility that at least some of it came from asteroid bombardment rather than being part of the original Earth-Moon system.

  9. We found those WMDs… on the Moon!

  10. T.E.L.

    Do a literature search. In the astrophysical journal George Pal Productions, an article titled Destination Moon predicted lunar uranium way back in 1950. I saw the article one Saturday morning along with two or three other articles in a row. I ate an entire bucket of corn just during the abstracts.

  11. MadScientist

    That’s awesome detecting uranium from so far away. :) I always imagined that some of the human lunar explorers had handheld geiger counters – if they had, I wonder what levels of radiation they were seeing. Geiger counters aren’t good for measuring energy though; you’d need a secondary electron emission instrument or something similar.

  12. What if it blows up, and sends the Moon into deep space? And here, we don’t even have a base there…..

    (yes, S1999 reference)

    J/P=?

  13. Check your spam filter- I linked the publication with the lunar prospector data and I think your web-bot considers the science magazine website to be spam.

  14. T.E.L.

    The presence of plutonium on the Moon was verified all the way back in 1969 by Pete Conrad and Alan Bean.

  15. Aside from the original earth-moon connection, a surprisingly (surprising to non-experts, I suppose) amount of the stuff laying around on the moon’s surface consists of more recently deposited bits and pieces of Earth, Mars and Venus.

  16. @4: No need. There is already an atomic death ray at the secret moonbase. Don’t look too closely!

  17. T.E.L.

    Naked Bunny,

    Are you related to Brad Guth?!!!

  18. Yousuf Khan

    Regarding your assertion that the Moon must’ve formed out of the ejecta of a collision between a young Earth and a Mars-sized, the so-called “Theia theory”, it’s not so sure anymore. They have now discovered water embedded in volcanic material on the Moon, which calls into question the Theia theory.

    http://preview.tinyurl.com/6d84r8

  19. Plutonium being from Pluto

    @ 14. T.E.L. :

    The presence of plutonium on the Moon was verified all the way back in 1969 by Pete Conrad and Alan Bean.

    Yeah I’ve been there too! ;-)

    I think we were talking about uranium actually but, yeah, that’s pretty cool (or should that be *hot*) too! :-)

    PS. BA did you ever write a post on that new element that was the latest one artificially made in labs a week or two ago?

    Plus, question : Could the LHC make more new artificial elements via atom-smashing too?

  20. Geophysicist

    It’s an interesting one to be sure. While Uranium is certainly a common element on Earth (more abundant than tin) economic, and therefore traceable concentrations tend to arise by circumstances one wouldn’t expect to find on the moon. Primary economic deposits are generally hosted within granites, which being less dense than surrounding rock when molten, intrude into the crust. This generally happens as a result of tectonic forces. Secondary sandstone and calcrete deposits rely on the erosion and deposition of primary sources.

    So while the moon is certainly granitic, I am still surprised that measurable uranium was detected. Perhaps it is a testament to the sensitivity of our instruments? Either way, it is a remarkable discovery.

  21. T.E.L.

    Plutonium being from Pluto Said:

    “Yeah I’ve been there too!”

    Heh, heh, heh…

  22. llewelly

    14. T.E.L. Says:
    June 29th, 2009 at 6:56 pm:

    The presence of plutonium on the Moon was verified all the way back in 1969 by Pete Conrad and Alan Bean

    Surprising that plutonium was confirmed first, considering that The longest-lived isotope of plutonium is plutonium-244 with a half-life of 80 million years.

  23. Adrian Lopez

    The prospector in that picture has no shadow! Finally… solid proof that the moon landings never happened!

    Well… either that, or no long winter this year.

  24. gruebait

    I’d be most curious about the composition of the regolith, stuff that could literally be scooped up off the surface and smelted. For a sustained presence, they are going to need bulk oxygen, water, cement, aluminum, stuff like that before they need berkelium or germanium.

  25. T.E.L.

    Adrian Lopez Said:

    “Well… either that, or no long winter this year.”

    I’m betting an entire dollar on that winter-thingy you just said.

  26. Alan French

    I wonder if the Moon landing conspiracy folks will grab onto that photo clearly showing a prospector on the lunar surface. Perhaps the “prospector” is really a special effects guy making sure the surface looks just right.

    Clear skies, Alan

  27. Gary Ansorge

    Naw. The prospector is just a bit of pereidolia (Dang, I never seem to be able to spell that right).
    Actually, it’s just a lump of carbon,,,

    Amazing sensitivity. How fraking low were they flying(cruising,er, orbiting,,,) anyway???
    I just keep wondering how big the supernova was that seeded this system. Must have been a real whopper (so many heavy elements).

    GAry 7

  28. TheElkMechanic

    Mining on the moon? They better bring a M.U.L.E. to haul the ore.

  29. JaWiB

    Been reading “The Moon is a Harsh Mistress”–my first Heinlein book–and it’s funny that he mentions they eventually find Uranium on the moon, and no one in the book expected it either.

  30. Brian Hart

    It so clear to me that that prospector inserted that fake astronaut onto the Moon’s surface. When will you all wake up and see that Vast Prospector Conspiracy to keep NASA away from the Moon??!!

  31. gar

    Uranium on the moon, eh? Nuclear power plants, eh? Well, you know what this means. Time for the SPACE: 1999 Conspiracy Theorists!

    Beware the 13th of September. . .!

  32. Torbjörn Larsson, OM

    They have now discovered water embedded in volcanic material on the Moon, which calls into question the Theia theory.

    But such questioning doesn’t seem to have any basis according to the reference you gave. They were happily considering that neither resulting material (Earth and Moon) were as hot as earlier suspected.

    Isn’t partial melting A Good Thing here? As a layman I perused the Wikipedia article, and there was some problem attributed to a fully melted Earth crust. (But perhaps new problems with a partial melt?)

    For consistency I seem to remember that a rather cool glancing blow (by, again, a 1:10 mass ratio impactor) is also what is proposed to explain the Mars surface (crustal?) dichotomy. (Though surely there are scaling issues here, higher masses imparts higher energy.) And a glancing blow would be most likely anyway, wouldn’t it?

  33. T. Poe

    I fully expect there to be movie (likely directed by Micheal Bay) which centers around the government sending a team of inexperienced, roguish, but driven individuals to the moon in order to stop a terrorist organization (in the form of the Not-al-Qaeda) from turning it into a single, massive nuclear bomb. In this movie people will fall rapidly down massive chasms, observe all the pretty stars while the Earth is in plain view, preform bank turns in space shuttles and finally someone will survive severe decompression with no ill effect other than being a bit short of breath.

    I greatly look forward to the inevitable Bad Astronomy review.

    On the other hand, this may hype moon exploration enough that the government might take a bit more interest in NASA. Anything that brings in a bit more cash for research can’t be all bad.

  34. With reference to some *ahem* lunacy a few weeks ago – did anyone think to ask the moon if we can exploit these findings?

  35. That’s amazing! I was wondering how its like to live on the moon?? but definitely, i would still go back to earth. Perhaps in the future if the prophecies will come to pass about earth, that it will be covered with water or will have an ice age, maybe the NASA can find ways to consider moon as human habitat..hmmm..Anyway, this is a great information and a very nice articles. ei, try posting this on http://www.freepressreleasecenter.com/ , where everyone can see this article..

    Marcus-

  36. Sili

    And it’s also how they found other elements like thorium, potassium, oxygen, magnesium, silicon, calcium, titanium, and iron, too.

    I thought that the lighter elements (without longlived unstable isotopes) were detected through their stimulated emission after bombardment with cosmic rays.

    (Psst – not that I care, but some is bound to point out the “also … too”.)

  37. Mang

    Just thinking about a Mars sized object hitting Earth resulting in the Moon. Since Mars is about twice the diameter of the Moon that leaves about 7/8ths of the volume unaccounted for.

    Now I wouldn’t expect it all to be present, but only 1/8th. The models they used must have accounted for it all somewhere. That seems like a lot to chuck into deep space.

  38. Gary Ansorge

    36. Mang:

    It’s a good possibility that the impactor experienced sufficient deceleration to cause it to drop into the sun, so there would be no remnants for us to discover,,,on the other hand,,,maybe it’s just in a 4.5 billion year orbit and getting ready to clobber us again.

    Hey Phil,,, Death from the Mars Impactor. A new book for Ya,,,(a thank you note in the intro will do fine, thanks,,,)

    Gary 7

  39. “For a sustained presence, they are going to need bulk oxygen, water, cement, aluminum, stuff like that before they need berkelium or germanium.”

    Just to nit-pick “Cement” can’t exist on the moon. Regular Portland Cement is derived from limestone. Limestone is made up of the skeletons of organisms like coral. These organisms need large oceans to grow in.

    So no Cement on the Moon, Mercury, or smaller asteroids.

    The regolith does have an interesting property that it hasn’t been smoothed down by air and water erosion so likes to stick together like gypsum and could be used in its raw form as drywall (it would just need to be compressed into the right shape) or if put in a microwave after being compressed the rough edges bond together making a hardened material that could be used in place of Concrete.

  40. Sir Eccles
  41. Stuart van Onselen

    Useful stuff, that regolith. But wouldn’t they need to take care that the stuff they build out of it is properly sealed, lest bits of it flake off? I remember reading somewhere that lunar dust is a right royal pain-in-the-you-know-where, getting into everything, abrading moving parts, and not being too nice on the lungs, either. Maybe even a bit like asbestos?

  42. Mang

    37. @Gary – no doubt arriving back on our doorstep in 2012.

  43. Greg in Austin

    I’m not sure, but something about that photo looks fake…

    8)

  44. firemancarl

    One of the key aspects of the Moon is that it’s not as dense as the Earth — in fact, it’s just a bit more than half the Earth’s density

    You mean until a chunk of a brown dwarf hits then impregnates the moon with super-duper-uber strong magnatisim! Duh!!!

    Wot? You didn’t watch ‘Impact’ the other night???

  45. Joe Meils

    Going back to post #10, about “Destination Moon”… as I recall, Joe (the comic relief radio/radar operator, gets the last line in when one of the scientists announces he may have found a deposit of uranium on the Moon…

    “Well, ain’t that dandy! Now we can blow up the moon, too!”

  46. Jim

    My moon-based Death Ray
    Panics the people of Earth
    Mock my theories now!

  47. J Earley

    I think that Geophysicist is on the right track here. Many ore deposits on Earth are the result of water, volcanic activity or even life (iron ore beds or limestone, for instance) While there are many areas of former volcanic activity on the Moon, we are not very likely to find concentrated ore deposits that require water to form, by minerals precipitating out of hot water as it cools. I believe that any water on the moon can be accounted for by cometary impacts
    As to the Mars sized impactor, I showed my students the results of a numeric simulation of the impact. Most of the material in the impactor gets incorporated into the forming Earth. Only a small part of it has enough angular momentum to make orbit. It was NOT an elastic collision!

  48. Lisa

    love your article but i’d like to point out what i believe is a misleading phrasing that you used. The gamma rays emitted that are picked up my radiation detection equipment (usually in space the high purity germanium detectors for surveying, but i have no proof that’s what was used here) are not the direct product of the Uranium itself ( the alpha can only be detected with low resolution at a few centimeters) The progeny emit a specific spectrum of higher energy gammas that can be traced to being uranium. A spectrum of gamma detection can be marked a signature for a specific radioactive elements. Two gammas? my guess is that the signature of Lead and Bismuth from the radium decay (a product of uranium decay, and the source of Radon in your home) would be sufficent evidence for the presence of naturally occuring uranium. Of course these products are the result of very long lived radioactive decays. The peak for finding uranium this way would be somewhere (i’m honestly not sure the exact number) in the range of a million years. Which would be just fine for finding it on the moon

  49. JoeSmithCA

    Too bad it is still so bleeping expensive to put things on the moon. I’m impatient, I want to put robotic construction vehicles up on the moon (even tiny ones) digging, mining and building a base.

  50. Gavin Mendeck

    I had to go check to be sure, but looks like the 1990s Lunar Prospector found evidence of uranium. Still, it’s great to have more data.

    “Elemental abundance values for O, Si, Ti, Al, Fe, Mg, Ca, U, and K were derived from LP gamma ray spectrometer [Feldman et al., 1999] observations acquired during the high-altitude portion of the LP mission. For the elements O, Si, Ti, Al, Fe, Mg, and Ca, the data are given in units of elemental weight percent. For the elements U and K, the data are given in units of ppm.”

    http://pds-geosciences.wustl.edu/missions/lunarp/reduced_special.html

  51. Saider72

    Mang,

    Since Mars is about twice the diameter of the Moon that leaves about 7/8ths of the volume unaccounted for.

    I also have noticed that they always indicate the size of the impactor, but nobody mentions how big the Earth was at that time. You assume that the Earth at that time was the same size as it is presently and that all the mass of the impactor ended up in the moon. My guess is that the models they used had a smaller (relative to the present mass) Earth getting hit by a Mars sized object. 7/8ths of the stuff aggregated back into the present Earth body, and the remainder formed the moon.

    Just a thought.

  52. Uranium is not more abundant than tin.

  53. For the record, I wrote the death ray poem quoted above by Jim. See:

    http://www.nada.kth.se/~asa/mad.html

  54. ZERO

    W00T!

    China plans to land a man on the Moon by 2017!

  55. Dave

    No surprise; considering John Lear says we and current inhabitants of the moon are currently mining there under the cloaked veil of secrecy.

  56. Jonny

    @Geophysicist, Granite is a phaneritic rock characterized by slow cooling right? Since the moon has no atmosphere and is directly exposed to space, this would act like an insulator given there are no particles to radiate heat into. Could granite and other phaneritic rocks then easily form on the surface? Maybe I’m missing a chicken or an egg here.

  57. John

    Gamma rays detected after the crash? Sound like they detected the power supply. Those things have plutonium in them

  58. Adam

    You can see a person in the background that doesn’t have a space suit on so the picture is fake.

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