Research Suggests Water Content Of Moon Interior Underestimated

WASHINGTON -- NASA-funded scientists estimate from recent research
that the volume of water molecules locked inside minerals in the
moon's interior could exceed the amount of water in the Great Lakes
here on Earth.

Scientists at the Carnegie Institution's Geophysical Laboratory in
Washington, along with other scientists across the nation, determined
that the water was likely present very early in the moon's formation
history as hot magma started to cool and crystallize. This finding
means water is native to the moon.

"For over 40 years we thought the moon was dry," said Francis McCubbin
of Carnegie and lead author of the report published in Monday's
Online Early Edition of the Proceedings of the National Academy of
Sciences. "In our study we looked at hydroxyl, a compound with an
oxygen atom bound with hydrogen, and apatite, a water-bearing mineral
in the assemblage of minerals we examined in two Apollo samples and a
lunar meteorite."

McCubbin's team utilized tests which detect elements in the parts per
billion range. Combining their measurements with models that
characterize how the material crystallized as the moon cooled during
formation, they found that the minimum water content ranged from 64
parts per billion to 5 parts per million. The result is at least two
orders of magnitude greater than previous results from lunar samples
that estimated water content of the moon to be less than 1 parts per
billion.

"In this case, when we talk about water on the moon, we mean water in
the structural form hydroxyl," said Jim Green, director of the
Planetary Science Division at NASA Headquarters in Washington. "This
is a very minor component of the rocks that make up the lunar
interior."

The origin of the moon is now commonly believed to be the result of a
Mars-sized object that impacted the Earth 4.5 billion years ago. This
impact put a large amount of material into Earth's orbit that
ultimately compacted to form the moon. The lunar magma ocean that is
thought to have formed at some point during the compacting process,
began to cool. During this cooling, water either escaped or was
preserved as hydroxyl molecules in the crystallizing minerals.

Previous studies found evidence of water both on the lunar surface and
inside the moon by using respectively, remote sensing data from the
Indian spacecraft Chandrayaan-1 and other lunar sample analysis.
Carnegie researchers looked within crystalline rocks called KREEP (K
for potassium; REE, for rare Earth elements; and P for phosphorus).
These rocks are a component of some lunar impact melt and basaltic
rocks.

"Since water is insoluble in the main silicates that crystallized, we
believed that it should have concentrated in those rocks," said
Andrew Steele of Carnegie and co-author of the report. "That's why we
selected KREEP to analyze."

The identification of water from multiple types of lunar rocks that
display a range of incompatible trace element signatures indicates
that water may be at low concentrations but ubiquitous within the
moon's interior, potentially as early as the time of lunar formation
and magma ocean crystallization.

"It is gratifying to see this proof of the hydroxyl contents in lunar
apatite," said lunar scientist Bradley Jolliff of Washington
University in St. Louis. "The concentrations are very low and,
accordingly, they have been until recently nearly impossible to
detect. We can now finally begin to consider the implications - and
the origin - of water in the interior of the moon."

The research was funded by the NASA Astrobiology, Mars Fundamental
Research, and the Lunar Advanced Science and Exploration Research
programs in NASA's Planetary Division in Washington.

For more information on NASA science programs, visit:

http://www.nasa.gov

Source: NASA