Solar wind particles likely source of water locked inside lunar soils

October 14, 2012
The Moon. Credit: NASA

The most likely source of the water locked inside soils on the moon's surface is the constant stream of charged particles from the sun known as the solar wind, a University of Michigan researcher and his colleagues have concluded.

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

In 2009, NASA's Lunar Crater Observation and Sensing satellite, known as LCROSS, slammed into a permanently shadowed and ejected a plume of material that was surprisingly rich in water ice. Water and related compounds have also been detected in the , the layer of fine powder and rock fragments that coats the lunar surface.

But the origin of lunar surface water has remained unclear. Is it mainly the result of impacts from water-bearing comets and other chunks of , or could there be other sources? Theoretical models of stability dating to the late 1970s suggest that (protons) from the can combine with oxygen on the moon's surface to form water and related compounds called hydroxyls, which consist of one atom of hydrogen and one of oxygen and are known as OH.

In an article published online Sunday in the journal Nature Geoscience, U-M's Youxue Zhang and colleagues from the University of Tennessee and the California Institute of Technology present findings that support solar-wind production of on the moon.

The first author of the paper is Yang Liu of U-T. She is a U-M alumna who earned her doctorate under Zhang, who is a professor in the Department of Earth and Environmental Sciences.

This is an agglutinate sample. Credit: David McKay.

In the paper, the researchers present and mass spectrometry analyses of Apollo samples that reveal the presence of significant amounts of hydroxyl inside glasses formed in the lunar regolith by 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 , 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."

The findings imply that ice inside permanently shadowed polar craters on the moon, sometimes called cold traps, could contain hydrogen atoms ultimately derived from the solar wind, the researchers report.

"This also means that water likely exists on Mercury and on asteroids such as Vesta or Eros further within our solar system," Liu said. "These planetary bodies have very different environments, but all have the potential to produce water."

The regolith glasses are called agglutinates, and the study reported in Nature Geoscience is the first to identify agglutinates as a new reservoir of OH on the moon—an "unanticipated, abundant reservoir" of OH and water in the lunar regolith, according to the authors.

The researchers analyzed individual grains from Apollo 11 mare soil, Apollo 16 highland soil and Apollo 17 mare soil. The grains included agglutinates and impact glasses.

Explore further: 3 questions: Ben Weiss discusses what a wet moon might mean

More information: DOI: 10.1038/ngeo1601

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1 / 5 (4) Oct 14, 2012
This is how "water ice" is created on both comets and situations such as Io and Enceladus. There is no need for fluffy snowballs or oceans to explain the abundance of 'water ice'.
3 / 5 (2) Oct 14, 2012
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

It would mean, the protons implanted would remove the oxygen from titanium oxide in lunar soil, thus forming the thermodynamically metastable mixture of metallic titanium and water. But we know, the metallic titanium reacts with water readily during heating under releasing of hydrogen back again. If such mechanism is the only source of hydroxyls in the lunar soil, it would mean, we cannot release the humidity from it anyway with heating, which would make the building of lunar base problematic.

Of course, with using of sufficiently high temperatures every compound can be decomposed into its elements, so we could separate the oxygen and hydrogen from lunar soil and use the titanium as a construction material - but such approach would be a way more energy hungry.
5 / 5 (2) Oct 14, 2012
Does this mean the (usable) water content is only available in a very thin crust? That would be good and bad (good, because the water is 'easy' to access, while bad meaning that there isn't a lot of it overall - and probably not enough concentrated in one place to make it viable as a long term source for any consumers on the Moon)

Anyways, the theory would be easy to test as digging down should lead to an exponential dropoff of the hydroxyl components thus formed.
5 / 5 (2) Oct 14, 2012
Does this mean the (usable) water content is only available in a very thin crust?
Yes, it would mean, that this "water" is strongly chemically bound, so it cannot migrate during repetitive heating and concentrate itself inside of deeper layers of lunar soil. But the recent findings of lunar craters at poles just point to reservoirs of the ice in the deeper layer of soil. Such a water couldn't originate by the above mechanism. Maybe the solar wind contains hydroxyl radicals by itself, which are formed with evaporation of water from comets falling into the Sun. These hydroxyle radicals - when trapped inside the lunar soil - would make the water content volatile and capable of accumulation into deeper layers of soil.
1 / 5 (4) Oct 14, 2012
Here is an article that discusses how the 'water' on comets is made, same as what is mentioned above. This article is from six years ago, science will eventually catch up with the 'Electric Universe'.

5 / 5 (5) Oct 14, 2012
http://www.thunde...act2.htm might even be more informative on the subject than cantdrive85 realizes.
4.2 / 5 (5) Oct 14, 2012
"http://www.thunde...act2.htm might even be more informative on the subject than cantdrive85 realizes."

Agreed. Strange how that link notes the absence of water on the *surface* of comets Halley, Borrelly and Wild 2 but totally ignores the detection of water in the coma of these comets:

http://www.ncbi.n...17773501 &cd=30&hl=en&ct=clnk&gl=us&client=firefox-a


That thunderdolts link even mentions jet phenomena in comets, which act to outgas known cometary constituents (such as water) from *beneath* their surfaces. Maybe EU claptrap will eventually catch up with actual observations.
5 / 5 (5) Oct 15, 2012
science will eventually catch up with the 'Electric Universe'

Middle School curriculum AD 2025
- physics - electric universe
- biology - creationism
- geography - flat-Earth geocentrism
- chemistry - alchemy
- math - Harry Potter magic

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