Ion Beam Materials Lab.
A team of scientists used an ion beam in a basement room at Los Alamos National Laboratory to simulate solar winds on the surface of the Moon. The table-top simulation helped confirm that the Moon is inherently dry.
In research published in Science Express, Zachary Sharp of the University of New Mexico and a team of scientists from California, Texas and New Mexico — including Yongqiang Wang, leader of Los Alamos’ Ion Beam Materials Lab — present an analysis of chlorine isotopic ratios in lunar rock samples that seem to indicate that the Moon never had water of its own.
Many scientists believe that the Moon formed when a large object collided with Earth early in its formative stages, leaving behind a blob of material that became trapped in orbit around the nascent Earth. Because most of the water on Earth likely came from water liberated from molten basalts as they cooled, researchers have often wondered whether the Moon’s geology contains similar concentrations of trapped water.
Sharp and his team examined ratios of stable chlorine isotopes — chlorine-35 and chlorine-37 — in terrestrial and lunar rock samples. Chlorine readily interacts with hydrogen and is highly volatile. Consequently, the ratio and concentrations of these isotopes can provide a “fingerprint” of water content of volcanic rocks.
If the Moon were formed via cataclysmic collision of a foreign body with a fledgling Earth, it’s reasonable to assume that lunar basalts would share a similarly soggy history as their earthen brethren. However, an analysis of the chlorine isotopic ratios of rocks from the Earth and Moon provided vastly different fingerprints. Sharp and his team came up with three possible explanations for the differences: 1) the moon-forming collision homogenized molten material from Earth and the colliding body into a material with a unique composition, 2) hydrogen-rich solar winds buffeting the moon preferentially stripped away one isotopic chlorine species from rocks, or 3) lunar basalts were inherently anhydrous.
The researchers dismissed the homogenization scenario after comparing observed chlorine isotope concentrations with other volatile elements in the basalts. The other volatile chemicals did not behave consistently with what would have been expected for the homogenization scenario.
To assess the effects of solar winds, Los Alamos researcher Wang took a thin film of sodium chloride — the same chemical as ordinary table salt — and bombarded it with a stream of protons (hydrogen ions) at Los Alamos’ Ion Beam Materials Lab. If the rocks were to be affected by the solar winds, the lighter chlorine isotope, chlorine-35, would preferentially react with the protons and be carried away as hydrogen chloride (HCl) gas. If this scenario were true, researchers would then find slightly higher ratios of the heavier isotope in the rocks. After subjecting the sample to eons of “solar-wind” exposure, the research team found that the samples were essentially unaffected by the proton onslaught.
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