There is water inside the moon – so much, in
fact, that in some places it rivals the amount of water found within the
Earth.
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.
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 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 Youxue Zhang, James R. O’Neil Collegiate
Professor of Geological Sciences.
The lunar highlands are thought to represent the original crust,
crystallized from a magma ocean on a mostly molten early moon. The new
findings indicate that the early moon was wet and that water 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
Zhang.
In 2008, laboratory measurement of Apollo lunar samples 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.
“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 crystalline
structure 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 moon’s
primordial crust. It was collected on the rim of Apur Crater during the
Apollo 15 mission.
Reference: Hejiu Hui et al., Water in lunar anorthosites and evidence
for a wet early Moon, Nature Geoscience, 2013, DOI: 10.1038/ngeo173.
In 2011, Brown University
scientists found super-tiny melt inclusions in lunar soil samples
--image top of page-- that opened the door for measurements that
revealed the magnitude of water inside the moon.
Image credit: Credit: Saal lab/Brown University
Source: The Daily Galaxy via University of Michigan
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