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October 16, 2012

Water locked in glass of lunar regolith

Researchers presented infrared spectroscopy and mass spectrometry analyses of Apollo samples that reveal the presence of significant amounts of hydroxyl inside glasses formed in the lunar regolith by micrometeorite impacts.

When combined, the techniques of Fourier transform infrared spectroscopy and secondary ion mass spectrometry can be used to determine the chemical form of the hydrogen in a substance, as well as its abundance and its isotopic composition. Most of the infrared spectroscopy work was done at Zhang's U-M lab, and the mass spectroscopy was conducted at Caltech.

"We found that the 'water' component, the hydroxyl, in the lunar regolith is mostly from solar wind implantation of protons, which locally combined with oxygen to form hydroxyls that moved into the interior of glasses by impact melting," said Zhang, the James R. O'Neil Collegiate Professor of Geological Sciences.

"Lunar regolith is everywhere on the lunar surface, and glasses make up about half of lunar regolith. So our work shows that the 'water' component, the hydroxyl, is widespread in lunar materials, although not in the form of ice or liquid water that can easily be used in a future manned lunar base.



This microscope image shows a grain of agglutinate glass similar to those analyzed in the lunar surface-water study reported in Nature Geoscience. The specimen in this image, which comes from samples returned by Apollo astronauts, is smaller than a typical dust grain. Image by Yang Liu.

Nature Geoscience - Direct measurement of hydroxyl in the lunar regolith and the origin of lunar surface water



Here is an analysis of how much hydroxyl is on the moon from a spacemath worksheet from NASA This was back when the assumption was that there was only hydroxyl in the top one millimeter which is what could be directly measured. I think the new work suggests the hydroxyl is more common and goes to deeper depths.

Complimentary data from the Deep Impact/EPOXI and Cassini missions of the rest of the lunar surface also detected hydroxyl molecules covering about 25% of the surveyed lunar surface. The hydroxyl molecule consists of one atom of oxygen and one of hydrogen, and because water is basically a hydroxyl molecule with a second hydrogen atom added, detecting hydroxyl on the moon is an indication that water molecules are also present.

How much water might be present? The M3 instrument can only detect hydroxyl molecules if they are in the top 1-millimeter of the lunar surface. The measurements also suggest that about 1 metric ton of lunar surface has to be processed to extract 1 liter (0.26 gallons) of water.

Problem 1 – The radius of the moon is 1,731 kilometers. How many cubic meters of surface volume is present in a layer that is 1 millimeter thick?

Answer: The surface area of a sphere is given by S = 4π r2 and so the volume of a layer with a thickness of L is V = 4π r2 L provided that L is much smaller than r.
V = 4 x (3.141) x (1731000)2 x 0.001 = 3.76 x 10^10 m3

Problem 2 – The density of the lunar surface (called the regolith) is about 3000 kilograms/meter3. How many metric tons of regolith are found in the surface volume calculated in Problem 1? Answer: 3.76 x 10^10 m3 x (3000 kg/m3) x (1 ton/1000 kg) = 1.13 x 1011 metric tons.

Problem 3 – The concentration of water is 1 liter per metric ton. How many liters of water could be recovered from the 1 millimeter thick surface layer if 25% of the surface contains water? Answer: 1.13 x 10^11 tons x (1 liter water/1 ton regolith) x 1/4 = 2.8 x 1010 liters of water.

How many gallons could be recovered if the entire surface layer were mined? (1 Gallon = 3.78 liters). Answer: 2.8 x 10^10 liters x (1 gallon / 3.78 liters) = 7.5 x 109 gallons of water or about 8 billion gallons of water.


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