[meteorite-list] Caltech Team Finds Evidence of Water in Moon Minerals

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 22 Jul 2010 11:36:30 -0700 (PDT)
Message-ID: <201007221836.o6MIaU27011221_at_zagami.jpl.nasa.gov>

July 21, 2010

Contact:
Jon Weiner
+1 (626) 395-3226
jrweiner at caltech.edu

CALTECH TEAM FINDS EVIDENCE OF WATER IN MOON MINERALS

That dry, dusty Moon overhead? Seems it isn't quite as dry as it's
long been thought to be. Although you won't find oceans, lakes, or
even a shallow puddle on its surface, a team of geologists at the
California Institute of Technology (Caltech), working with colleagues
at the University of Tennessee, has found structurally bound hydroxyl
groups (i.e., water) in a mineral in a lunar rock returned to Earth by
the Apollo program.

Their findings are detailed in this week's issue of the journal Nature.

"The Moon, which has generally been thought to be devoid of hydrous
materials, has water," says John Eiler, the Robert P. Sharp Professor
of Geology and professor of geochemistry at Caltech, and a coauthor on
the paper.

"The fact that we were able to quantitatively measure significant
amounts of water in a lunar mineral is truly surprising," adds lead
author Jeremy Boyce, a visitor in geochemistry at Caltech, and a
research scientist at the University of California, Los Angeles.

The team found the water in a calcium phosphate mineral, apatite,
within a basalt collected from the Moon's surface by the Apollo 14
astronauts.

To be precise, they didn't find "water" -- the molecule H2O. Rather,
they found hydrogen in the form of a hydroxyl anion, OH-, bound in the
apatite mineral lattice.

"Hydroxide is a close chemical relative of water," explains coauthor
George Rossman, Caltech's Eleanor and John R. McMillan Professor of
Mineralogy. "If you heat up the apatite, the hydroxyl ions will
'decompose' and come out as water."

The lunar basalt sample in which the hydr
collected by the Apollo 14 Moon mission in 1971; the idea to focus the
search for water on this particular sample was promoted by Larry
Taylor, a professor at the University of Tennessee in Knoxville, who
sent the samples to the Caltech scientists last year.

"The Moon has been considered to be bone dry ever since the return of
the first Apollo rocks," Taylor notes. However, there are lunar
volcanic deposits interpreted as having been erupted by expanding
vapor. Although carbon dioxide and sulfur gases have generally been
thought to dominate the expanding vapor, recent evidence from the
study of the these deposits has suggested that water could also play a
role in powering lunar volcanic eruptions. The discovery of hydroxyl
in apatite from lunar volcanic rocks is consistent with this
suggestion.

The idea of looking for water in lunar apatite isn't new, Boyce notes.
"Charles B. Sclar and Jon F. Bauer, geoscientists at Lehigh
University, first noted that something was missing from the results of
chemical analyses of apatite in 1975," he says. "Now, 35 years later,
we have quantitative measurements -- and it turns out, they were
right. The missing piece was OH."

The Caltech team analyzed the lunar apatite for hydrogen, sulfur, and
chlorine using an ion microprobe, which is capable of analyzing
mineral grains with sizes much smaller than the width of a human hair.
This instrument fires a focused beam of high-energy ions at the sample
surface, sputtering away target atoms that are collected and then
analyzed in a mass spectrometer. Ion microprobe measurements
demonstrated that in terms of its hydrogen, sulfur, and chlorine
contents, the lunar apatite in this sample is indistinguishable from
apatites from terrestrial volcanic rocks.

"We realized that the Moon and the Earth were able to make the same
kind of apatite, relatively rich in hydrogen, sulfur and chlorine,"
Boyce says.

Does that mean the Moon is as awash in water as our planet? Almost
certainly not, say the scientists.
Moon must contain to be capable of generating hydroxyl-rich apatite
remains an open question. After all, it's hard to scale up the amount
of water found in the apatite -- 1600 parts per million or 0.16
percent by weight -- to determine just how much water there is on the
lunar landscape. The apatite that was studied is not abundant, and is
formed by processes that tend to concentrate hydrogen to much higher
levels than are present in its host rocks or the Moon as a whole.

"There's more water on the Moon than people suspected," says Eiler,
"but there's still likely orders of magnitude less than there is on
the Earth."

Nonetheless, the finding is significant for what it implies about our
Moon's composition and its history. "These findings tell us that the
geological processes on the Moon are capable of creating at least one
hydrous mineral," Eiler says. "Recent spectroscopic observations of
the Moon showed that hydrogen is present on its surface, maybe even as
water ice. But that could be a thin veneer, possibly hydrogen brought
to the Moon's surface by comets or solar wind. Our findings show that
hydrogen is also part of the rock record of the Moon, and has been
since early in its history."

Beyond that, Eiler continues, "it's all a great big question mark. We
don't know whether these were igneous processes," -- in which rocks
are formed by solidification of molten lava -- "or metamorphic" -- in
which minerals re-crystallize or change in change in chemistry without
melting. "They're both on the table as possible players."

?????????????????????????? # # #

In addition to Boyce, Eiler, Rossman, and Taylor, other authors on the
Nature paper, "Lunar apatite with terrestrial volatile abundances,"
include Research Assistant Professor Yang Liu from the University of
Tennessee in Knoxville; Edward Stolper, Caltech's William E. Leonhard
Professor of Geology, and Yunbin Guan, manager of Caltech's ion
microprobe laboratory. Their work was funded by grants from NASA's
Cosmochemistry Pro
Gordon and Betty Moore Foundation.

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http://media.caltech.edu.
Received on Thu 22 Jul 2010 02:36:30 PM PDT