Water on the moon: It's been there all along

Feb 18, 2013
Water on the moon: It’s been there all along
Called the "Genesis Rock," this lunar sample of unbrecciated anorthosite collected during the Apollo 15 mission was thought to be a piece of the moon's primordial crust. In a paper published online Feb. 17 in Nature Geoscience, a University of Michigan researcher and his colleagues report that traces of water were found in the rock. Credit: NASA/Johnson Space Center

Traces of water have been detected within the crystalline structure of mineral samples from the lunar highland upper crust obtained during the Apollo missions, according to a University of Michigan researcher and his colleagues.

The highlands are thought to represent the original crust, crystallized from a on a mostly molten early moon. The new findings indicate that the early moon was wet and that there was not substantially lost during the moon's formation.

The results seem to contradict the predominant lunar formation theory—that the moon was formed from debris generated during a giant impact between Earth and another planetary body, approximately the size of Mars, according to U-M's Youxue Zhang and his colleagues.

"Because these are some of the oldest rocks from the moon, the water is inferred to have been in the moon when it formed," Zhang said. "That is somewhat difficult to explain with the current popular moon-formation model, in which the moon formed by collecting the hot ejecta as the result of a super-giant impact of a martian-size body with the proto-Earth.

"Under that model, the hot ejecta should have been degassed almost completely, eliminating all water," Zhang said.

A paper titled "Water in lunar anorthosites and evidence for a wet early moon" was published online Feb. 17 in the Geoscience. The first author is Hejiu Hui, postdoctoral research associate of civil and environmental engineering and at the University of Notre Dame. Hui received his doctorate at U-M under Zhang, a professor in the Department of Earth and Environmental Sciences and one of three co-authors of the Nature Geoscience paper.

Over the last five years, spacecraft observations and new lab measurements of Apollo lunar samples have overturned the long-held belief that the moon is bone-dry.

In 2008, laboratory measurement of Apollo by ion microprobe detected indigenous hydrogen, inferred to be the water-related chemical species hydroxyl, in lunar volcanic glasses. In 2009, NASA's Lunar Crater Observation and Sensing satellite, known as LCROSS, slammed into a permanently shadowed lunar crater and ejected a plume of material that was surprisingly rich in water ice.

Hydroxyls have also been detected in other volcanic rocks and in the lunar regolith, the layer of fine powder and rock fragments that coats the lunar surface. Hydroxyls, which consist of one atom of hydrogen and one of oxygen, were also detected in the lunar anorthosite study reported in Nature Geoscience.

In the latest work, Fourier-transform infrared spectroscopy was used to analyze the water content in grains of plagioclase feldspar from lunar anorthosites, highland rocks composed of more than 90 percent plagioclase. The bright-colored highlands rocks are thought to have formed early in the moon's history when plagioclase crystallized from a magma ocean and floated to the surface.

The infrared spectroscopy work, which was conducted at Zhang's U-M lab and co-author Anne H. Peslier's lab, detected about 6 parts per million of water in the lunar anorthosites.

"The surprise discovery of this work is that in lunar rocks, even in nominally water-free minerals such as plagioclase feldspar, the water content can be detected," said Zhang, James R. O'Neil Collegiate Professor of Geological Sciences.

"It's not 'liquid' water that was measured during these studies but hydroxyl groups distributed within the mineral grain," said Notre Dame's Hui. "We are able to detect those hydroxyl groups in the of the Apollo samples."

The hydroxyl groups the team detected are evidence that the lunar interior contained significant water during the moon's early molten state, before the crust solidified, and may have played a key role in the development of lunar basalts. "The presence of water," said Hui, "could imply a more prolonged solidification of the lunar magma ocean than the once-popular anhydrous moon scenario suggests."

The researchers analyzed grains from ferroan anorthosites 15415 and 60015, as well as troctolite 76535. Ferroan anorthosite 15415 is one the best known rocks of the Apollo collection and is popularly called the Genesis Rock because the astronauts thought they had a piece of the 's primordial crust. It was collected on the rim of Apur Crater during the Apollo 15 mission.

Rock 60015 is highly shocked ferroan anorthosite collected near the lunar module during the Apollo 16 mission. Troctolite 76535 is a coarse-grained plutonic rock collected during the Apollo 17 mission.

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Anda
3 / 5 (1) Feb 18, 2013
Too much assumptions. Still a lot to investigate and learn about this.
philw1776
1 / 5 (5) Feb 18, 2013
The settled science of the moon's origin takes another hit. Then again tweaking the theory wherein a early solar system comet bombardment brought water to quickly cooled moon might save it.

If there's one thing we learned from Kepler and the spectroscopically detected hot Jupiters, our 20th century models of how the solar system was formed were completely inadequate to mirror reality.
Tangent2
1 / 5 (5) Feb 18, 2013
For over 40 years, they have had the opportunity to study these samples/rocks in detail with every piece of high tech equipment that they could get there hands on. And still, they completely fail to find any water indicators. Now all of a sudden, they find it.

Why the sudden change in data?? Did they find a new tech to analyze the sample?

Also, one more reason why you never take a theory as fact, no matter how long the theory has been around. Age is not proof.
Sinister1811
1 / 5 (5) Feb 19, 2013
The fact that the moon has frozen water at its poles is old news. This will, in no doubt, come as an asset for future moon colonists.
Torbjorn_Larsson_OM
not rated yet Feb 19, 2013
The initial water content of Earth mantle would be something like 500 ppm (~ 0.05 % water by mass) and the initial water content of Mars mantle was similar (IIRC ~ 150 ppm). That Moon would have something similar (1/100 from dewatered magmatic rocks) shouldn't surprise anyone.

We know from zink isotopes that there was a large-scale evaporation of volatiles (eg zink) on the Moon, indicative of an impact formation. Lately the access to high capacity simulations have reformed [sic] the field, with many possible pathways to a Moon with similar isotope ratios for refractories (tungsten, chromium and titanium) as well as oxygen (and so water) as the Earth. [ http://docmadhatt...oon.html ]
Torbjorn_Larsson_OM
not rated yet Feb 19, 2013
[cont] Interestingly the likeliest scenario, that of two similar sized planetoids under low velocity impact, starts out with little to no rotation. That is also the best initial conditions for getting Vesta's two major impact craters (Venenia & Rheasilvia) correct. [ http://arstechnic...d-vesta/ ] It seems random aggregation leaves bodies with little to no rotation, it is impacts that gets the ball rolling.
Torbjorn_Larsson_OM
not rated yet Feb 19, 2013
@philw: There was never anything "settled" about Moon formation. The impact hypothesis was, and remains, the likeliest. But if, and exactly how, an impact formed the Moon is not tested yet. Here are the 5 serious contenders: fission, capture, condensation, collision, ejection. [ http://csep10.phy...ion.html ]

"Generally, work over the last 10 years has essentially ruled out the first two explanations and made the third one rather unlikely. At present the fifth hypothesis, that the Moon was formed from a ring of matter ejected by collision of a large object with the Earth, is the favored hypothesis; however, the question is not completely settled and many details remain to the accounted for."
Torbjorn_Larsson_OM
1 / 5 (1) Feb 19, 2013
@Tangent: "They" didn't fail to find water, they assumed for good reasons (no vacuum handling) it was contamination. It had to wait for modern sample methods to uncover the crystal water, which is why they look at hydrogen, see the article.
"In August 1976, a Soviet rocket landed on the moon, drilled six feet into the surface, extracted about half a pound of rock and flew back. In the rocks that it brought back, water made up around 0.1%."
"Nasa's Clementine mission bounced radio waves off the surface of the moon in 1994, and found evidence of water. Arlin Crotts at Columbia University in New York city says, 'No other author has ever cited the Luna 24 work.'"
"http://www.dailym...ry.html"

As for the rest, you are confusing observation with theory. A well tested theory (Moon water) is more solid than any ad hoc observation (Apollo rock water).