[meteorite-list] New look at Apollo moon rocks reveals signs of 'native' water

From: Galactic Stone & Ironworks <meteoritemike_at_meteoritecentral.com>
Date: Mon, 18 Feb 2013 14:25:01 -0500
Message-ID: <CAKBPJW-20s5rE3JPb2dv0Sbi4A9wjCY-c+UtJAaBs9vt0G6FkA_at_mail.gmail.com>

http://www.latimes.com/news/nationworld/nation/la-sci-moon-water-20130216,0,4987754.story


By Amina Khan, Los Angeles Times

February 17, 2013, 6:29 p.m.

Scientists picking up signs of water on the moon's surface typically
attribute them to deposits left by comets, asteroids and other
heavenly objects. But a new analysis of lunar samples brought back to
Earth by Apollo astronauts in the early 1970s indicates that the
moon's interior may have been a little damp in its early days.

The findings, published online Sunday in the journal Nature
Geoscience, support mounting evidence that the moon once contained
some "native" water ? throwing a wrench into current beliefs about how
Earth's companion formed.

Prevailing theories hold that the moon was created when a Mars-sized
body crashed into the young Earth and broke off debris that eventually
coalesced into a new entity. In the process, much of the water would
have evaporated into space, leaving Earth's new satellite quite arid.

PHOTOS: Images of space

"It's thought that the moon's formation involved the materials getting
very hot," said Paul Warren, a UCLA cosmochemist who was not involved
in the new study. "It's usually assumed that little water would have
survived through that."

Indeed, the samples returned by the Apollo missions that visited the
lunar highlands seemed to confirm that Earth's cold, rocky companion
was bone-dry, said University of Notre Dame geologist Hejiu Hui, who
led the new analysis.

But work in the last five years has challenged that notion, as
scientists have used more advanced methods to look for increasingly
tiny concentrations of water in glass beads that are thought to have
been formed by volcanic eruptions in the moon's early days.

Some experts have argued that those glass beads could have been
exposed to alien water sources after they had been ejected from the
moon's interior. So Hui and his colleagues decided to look at a type
of rock called plagioclase, which is thought to have formed in a magma
ocean inside the moon. Although the rocks later floated to the surface
to form the crust, they contain a chemical time capsule from inside
the young moon.

To further rule out any outside source of water, Hui's team looked
past the surface of these rocks and into their centers.

After examining the samples under a microscope equipped with a
spectrometer, the researchers found that the rocks contained 6 parts
per million of water. That?s drier than an Earth desert, but far more
than expected to survive in a rock from the moon's once-molten center.

The samples should have been bone-dry, Hui said, but "somehow we still
detect this amount of water, so that makes things interesting."

Based on their measurements, the researchers estimated that the early
moon's magma ocean could have contained up to 320 parts per million of
water. Once that ocean mostly crystallized, the remaining residues
could have had as much as 1.4% water. That could explain the measured
water content in lunar rocks, Hui said.

The findings could have interesting implications for theories about
how the moon came to be, Warren said.

"It's thought that the moon's formation involved the materials getting
very hot, and it's usually assumed that little water would have
survived through that," he said. If the new study is right, "It opens
up quite a mystery as to how the moon came through what we think was a
very hot genesis process with this much water."

The findings also have implications for the moon's geological
evolution, Warren said. Researchers have reconstructed the history of
the moon's crustal formation while assuming there were negligible
amounts of water involved. Now scientists may need to reevaluate some
of those ideas.

Knowing how much water there is could be handy for future explorers.
"Someday, when we put men on the moon in a more permanent way, we
might need that water," Warren said.

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Received on Mon 18 Feb 2013 02:25:01 PM PST