First Conclusive Signature for Lunar Uranium
Written by Nancy Atkinson
Data from Kaguya's GRS. Credit: JAXA
Using data obtained from the gamma ray spectrometer on the Kaguya spacecraft scientists have found signatures of uranium, an element not seen in previous moon-mapping efforts. In addition to uranium, the Kaguya GRS data also is showing clear signatures for thorium, potassium, oxygen, magnesium, silicon, calcium, titanium and iron.
"We've already gotten uranium results, which have never been reported before," said Robert C. Reedy, senior scientists at the Planetary Science Institute. "We're getting more new elements and refining and confirming results found on the old maps."
Earlier gamma-ray spectrometer maps from the Apollo and Lunar Prospector missions show a few of the moon's chemical elements. But the maps constructed by Reedy and the Kaguya GRS team — using data gathered by state-of-the-art high-energy-resolution germanium detectors — are extending the earlier results and improving our understanding of the moon's surface composition.
Reedy and his colleagues are using measurements from the Kaguya lunar orbiter's GRS to construct high-quality maps of as many chemical elements as possible. Kaguya was launched in September 2007 and crashed into the moon at the end of its mission on June 10 of this year.
Source: Planetary Science Institute
Filed under: Moon
Tags: MoonRelated stories on Universe Today
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June 30th, 2009 at 5:37 am
According to Wikipedia:
"Uranium: Along with all elements having atomic weights higher than that of iron, it is only naturally formed in supernovas. The decay of uranium, thorium, and potassium-40 in the Earth's mantle is thought to be the main source of heat that keeps the outer core liquid and drives mantle convection, which in turn drives plate tectonics."
Which is interesting.
I'm wondering if moon samples of uranium could verify or dispute the giant impact hypothesis. The half-life of uranium-238 is about 4.47 million years. Which pretty much gives us a benchmark for the age of the earth and thus everything else.
So far, this benchmark has only been based on Uranium found on earth, it might be interesting to compare the half life decay of moon samples.
Can it be different?
I'm no expert, just curious. Anyone else have thoughts on this?
Damian K
June 30th, 2009 at 8:13 am
Other benchmarks for the age of the Solar System have come from returned moon rock samples, meteorite samples from Vesta and Mars and other meteorite samples, many from unknown sources, If memory serves I think we can get a date from the sun also, but you need to look that one up to see what exactly it is.
The half life decay rate for U 238 should be the same where ever the sample is from, Earth, Mars etc.
The age the rock formed as in lithofied would give us a lower end of the impact date in the impact theory, but this has already been inferred from the Apollo and Lunahood Samples.
The most interesting thing from this article is the very fact uranium has been detected on the moon, surly other reason/excuse (depending on viewpoint) to go there.
June 30th, 2009 at 8:29 am
Maybe tht's whay China wants to go to the Moon so badly? (jk)
If a meteorite hits an area where Uranium is considerable, couldn't it cause a nuclear reaction? Large meteorites tend to make a big bang anyway. It would be interesting to see if the shape and chemical makeup of craters can determine this.
I'm sure it can provide clues as to what actually happens during a large impact.
June 30th, 2009 at 1:25 pm
Dark Gnat Says
"If a meteorite hits an area where Uranium is considerable, couldn't it cause a nuclear reaction? Large meteorites tend to make a big bang anyway. It would be interesting to see if the shape and chemical makeup of craters can determine this."
I'm no expert but I think for a nuclear reaction to occur the Uranium has to be the 235 isotope, and refined. You also need a lump of pure uranium exceeding the critical mass for nuclear reactions.
It is really interesting that the uranium is there if the Moon did originate from the Earth's mantle. Did it come from impactors? The freightage would be high to get it back to Earth.
July 1st, 2009 at 4:28 am
No, and not by much.
A nuclear reaction is usually a fusion. It can also be a radioactive reaction (but not all of them), cleaving off parts of the nucleus. Some of these are fissions, i.e. cleaving into comparable parts. U238 is fissionable, can fission, but is not fissile, can not sustain a nuclear chain reaction. (Because it isn't fissionable by irradiation of neutrons of a very wide range of energies.)
As regards concentration, consider the Oklo reactor: "A key factor that made the reaction possible was that, at the time the reactor went critical, the fissile isotope 235U made up about 3% of the natural uranium, which is comparable to the amount used in some of today's reactors. (The remaining 97% was non-fissile 238U.) Because 235U has a shorter half life than 238U, and thus decays more rapidly, the current abundance of 235U in natural uranium is about 0.7%. A natural nuclear reactor is therefore no longer possible on Earth.
The Oklo uranium ore deposits are the only known in which natural nuclear reactors existed. Other rich uranium ore bodies would also have had sufficient uranium to support nuclear reactions at that time, but the combination of uranium, water and physical conditions needed to support the chain reaction was unique to the Oklo ore bodies." [Wikipedia.]
So ~ 3 % purity is enough for the controllable "delayed supercritical" chain reactions of a reactor. However, if you want a fast "prompt supercritical" chain reaction, a bomb, you want to go to purer material.
Since the Moon as opposed to the Earth hasn't separated out much thermally, no plate tectonics for example, there are likely no pure mineral ores of any kind. There would be no bomb, and if you want to extract the dispersed uranium you would have real use for all that solar energy for free!
AFAIU the great impactor theory is that the Moon is mostly crust, and that the impactor atmosphere and core mostly ended up on Earth. That would be consistent with uranium, which according to commenters on Bad Astronomy blog neither is especially dissoluble into the iron core nor is expected to end up deep since it readily forms light oxides. Um, U2O7, I think. Which is presumably why on Earth you find uranium on top, in the crust.
How about solar power driven linear accelerators?