Last fall, researchers, including Larry Taylor, a distinguished professor in the Department of Earth and Planetary Sciences, discovered “lunar dew” on the moon’s surface — absorbed “water” in the uppermost layers of lunar soil. This discovery of water debunked beliefs held since the return of the first Apollo rocks that the moon was bone-dry.
Now, scientists, including Taylor and Yang Liu, research assistant professor in the Department of Earth and Planetary Sciences, have discovered that water on the moon is more widespread — on the outside and inside of the moon — with some similarities to water in volcanic systems on Earth.
Featured in the article, “Lunar Apatite with Terrestrial Volatile Abundances” in the July 22 edition of the scientific journal, Nature.
The Moon is thought to be depleted relative to the Earth in volatile elements such as H, Cl and the alkalis. Nevertheless, evidence for lunar explosive volcanism has been used to infer that some lunar magmas exsolved a CO-rich and CO2-rich vapour phase before or during eruption. Although there is also evidence for other volatile species on glass spherules, until recently there had been no unambiguous reports of indigenous H in lunar rocks. Here we report quantitative ion microprobe measurements of late-stage apatite from lunar basalt 14053 that document concentrations of H, Cl and S that are indistinguishable from apatites in common terrestrial igneous rocks. These volatile contents could reflect post-magmatic metamorphic volatile addition or growth from a late-stage, interstitial, sulphide-saturated melt that contained ~1,600 parts per million H2O and ~3,500 parts per million Cl. Both metamorphic and igneous models of apatite formation suggest a volatile inventory for at least some lunar materials that is similar to comparable terrestrial materials. One possible implication is that portions of the lunar mantle or crust are more volatile-rich than previously thought.
9 pages of supplemental information
Thin slice of lunar basalt with a petrographic (geologic) microscope. This is the same view with crossed polarizers, revealing the complicated chemistry of the lunar minerals.The existence of volcanoes on the moon more than 4 billion years ago gave the researchers a clue that water might exist inside the body, since the dynamics of volcanoes on Earth are mostly driven by water. Therefore, the scientists made their novel discovery by examining a lunar basalt brought back from the 1971 Apollo 14 mission. Using secondary ion mass spectrometry at the California Institute of Technology in Pasadena, Calif., scientists determined volatile elements in a calcium phosphate mineral are very similar in the same mineral found on Earth.
The scientists said this provides “robust evidence for the presence of water in the interior of the moon from where some lunar rocks were derived. This demonstrates a closer chemical and geologic relationship between the Earth and moon than previously known. We must now re-evaluate the volatile inventories of the moon, relative to the Earth.”
The finding of volatiles on the moon has deep implications for how it, and the Earth, formed. It is generally believed that the moon was created when the early Earth was hit by a Mars-sized proto-planet called Theia, melting and vaporizing itself and a large chunk of the Earth. The cloud of particles created by the impact later congealed to form the moon, which supposedly was devoid of highly volatile elements such as hydrogen and chlorine. However, the researchers’ discovery of these volatiles challenges this theory.
“If water in the Moon was residue water kept during the giant impact, it is surprising that water survived the impact at all because less volatile elements, such as sodium and potassium, are strongly depleted. The details of the impact theory need to be re-examined,” Liu said.
The discovery of abundant and ubiquitous water on the moon could mean a human settlement on the moon is not so far-fetched. Currently, the endeavour would be very expensive. For example, it costs $25,000 to take one pint of water to the moon. However, if scientists devise processes to easily recover this water from the lunar rocks for drinking water and fuel, a human settlement is not out of reach.
“Now we have ready sources of water that can be consumed by plants and humans but also electrolyzed into liquid hydrogen and liquid oxygen to develop rocket fuel,” Taylor said. “Until the recent discovery of water in and on the moon, it was going to be a very energy-intensive endeavor to separate these elements from the lunar rocks and soil.”
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