Genuine
moon water has been found for the first time in rocks that were brought back to
Earth during NASA's historic Apollo missions 40 years ago. The water is
similar to that detected in comets, suggesting that the moon's scarce supply got
there through the impacts of these icy bodies.
To
determine where this moon
water came from, researchers studied thin slices of rocks collected by
astronauts in the 1970s using several kinds of microscopes. Under examination
was the ratio of hydrogen – two atoms of which bind with oxygen to make a water
molecule – to a rare version of hydrogen called deuterium.
James
Greenwood, a planetary scientist at Wesleyan University and lead author of a
new paper describing the results, said he and his colleagues discovered that
the levels of the deuterium isotope in moon water are double that of Earth's
and "not from this planet."
"This
is cometary
water and not the same-old water we have on Earth," said study co-author
Lawrence Taylor, a planetary geochemist at the University of Tennessee.
Watery
deliveries
The
Apollo moon rock water is the latest in a recent string of discoveries of water
and ice on the lunar surface.
Last
week, scientists announced that more than 600 million tons of moon
water ice is lurking at the bottom of dark craters at the lunar north pole.
Water vapor was also spotted during the intentional crash of two NASA probes
into similarly shadowed craters at the moon's south pole in October.
Observations
from several NASA and international probes have also found the chemical
signature for water across other regions of the moon. But the first detection
of lunar water, though in soil rather than inside a rock, came two years ago in
volcanic
glass beads.
Exposure
of those samples to the solar wind, or particles from the sun, on the moon's
surface renders their deuterium-hydrogen ratio difficult to determine, Greenwood
said, making a stab at the origin of their water guesswork.
Traces
of water had turned up in Apollo rocks previously, but Taylor and others had
shown this water to be a result of contamination from terrestrial water.
Impacts
from comets likely dumped unearthly water on the moon some four billion years
ago when many of the moon's
craters were gouged out. Earth also took a beating, and a small amount of
our planet's water came from the skies as well.
An
alternative scenario for the new hydrogen readings is that some regular hydrogen
blew off the moon as it formed, depleting amounts of it compared to deuterium,
Greenwood noted, but that it is too soon to tell.
Moon's
wet history
The
new finding of bona-fide lunar water in this first set of Apollo rocks will
help update historical water estimates for the moon, according to the study.
And
continued work could have big implications for lunar geology which may explain
puzzling density differences of lunar minerals compared to those on earth.
"Just a little water," Taylor said, can dramatically change how rocks form and
age. "This is a precursory examination that has shown startling things," Taylor
added.
This
announcement of water in lunar rocks follows on the heels of its recent detection
by orbiting probes including India's Chandrayaan-1 and by NASA's LCROSS mission
last fall.
"I
think we are embarking into a new era of looking at a wet moon," Greenwood told
SPACE.com. "Everything will have to be rethought."
The
research was presented at the 41st Lunar and Planetary Science Conference in
Texas last week.
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