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Traces of water within Apollo moon rocks challenge current lunar formation theory

A University of Michigan researcher and his colleagues have detected traces of water within moon rocks brought back to Earth during the Apollo missions. The moon rocks are part of the upper crust from the lunar highlands, which are thought to represent the original crust. Their findings suggest that the early moon was wet.

University of Michigan’s Youxue Zhang and his colleagues contend that their findings appear to contradict the predominant lunar formation theory – that the moon formed by gathering the hot ejecta as the result of a massive impact between Earth and another planetary body.

Under the predominant lunar formation theory, Zhang notes, the hot ejecta should have been “degassed almost completely, eliminating all water.”

Spacecraft data and new lab measurements of Apollo lunar samples have only recently rejected the long-held belief that the moon is completely dry.

In 2008, for example, laboratory measurement of Apollo lunar samples by ion microprobe found indigenous hydrogen, understood to be the water-related chemical species hydroxyl, in lunar volcanic glasses. A year later, NASA’s Lunar Crater Observation and Sensing satellite crashed into a lunar crater and ejected a plume of material that was rich in water ice.

Researchers used Fourier-transform infrared spectroscopy to examine the water content in grains of plagioclase feldspar from lunar anorthosites. These highland rocks are believed to have formed early in the moon’s history. Zhang and his colleagues detected about 6 parts per million of water in the lunar anorthosites.

Hejiu Hui, a postdoctoral research associate of civil and environmental engineering and earth sciences at the University of Notre Dame, points out that it is not “‘liquid’ water that was measured during these studies but hydroxyl groups distributed within the mineral grain.”

Researchers note that hydroxyl groups the team found are evidence that the lunar interior contained significant water during the moon’s early molten state. Hui adds that the discovery “could imply a more prolonged solidification of the lunar magma ocean than the once-popular anhydrous moon scenario suggests.”

Researchers examined grains from ferroan anorthosites 15415 and 60015, in addition to troctolite 76535. Ferroan anorthosite 15415 is also known as the Genesis Rock because the astronauts believed they had a piece of the moon’s primordial crust.

On August 1, 1971, Apollo 15 missions commander David R. Scott relayed the following message to Mission Control: “Guess what we just found! I think we found what we came for.” 

Scott was referring to the Genesis Rock, which geologists later concluded was about 4 billion years old.

The study’s findings were published online in the journal Nature Geoscience.