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Compared to Earth, the
moon appears to be perfectly dry

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and airless, but in fact it
possesses an extremely sparse

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atmosphere, barely
thicker than a vacuum.

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From late 2013 to early 2014,
a NASA mission called LADEE

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explored the lunar
atmosphere and dust environment.

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Now, LADEE's observations have
led to a new discovery about the

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moon's water.

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During the initial exploration
of the moon, and the analysis of

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all the returned samples
from the Apollo and the Luna

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missions, we thought that the
surface of the moon was dry.

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But more recent missions, like
Lunar Prospector, LCROSS, and

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Lunar Reconnaissance Orbiter,
have not only shown that the

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surface of the moon has a
global hydration, but there are

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actually high concentrations
of ice water in the permanently

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shadowed regions
of the lunar poles.

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In the decades following the
Apollo program, a series of

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robotic explorers revealed
tantalizing hints of water on

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the moon, challenging the
conclusion that the moon was

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dry.

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The first definitive discovery
of water was made in 2008 by the

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Indian mission Chandrayaan-1,
which detected hydroxyl

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molecules spread across the
lunar surface and concentrated

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at the poles.

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The following year, NASA's
LCROSS mission deliberately

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impacted part of its launch
vehicle into the southern crater

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Cabeus, ejecting a plume
that contained water ice.

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These discoveries showed that
the moon harbors water, and that

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the highest concentrations occur
within darkened craters at the

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poles.

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But questions remained about the
abundance of water at the moon's

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mid latitudes.

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Now, data from LADEE are
beginning provide answers.

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What we discovered is that the
surface releases its water when

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the moon is bombarded
by micrometeoroids.

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This is especially noticeable
during meteor showers.

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What we also found is that the
surface that's releasing the

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water is being protected by a
layer, a few centimeters of dry

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soil that can only be breached
by large micrometeoroids.

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When micrometeoroids impact the
surface of the moon, most of the

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material in the
crater is vaporized.

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There is also a shock wave
that propagates outward.

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That shock wave carries enough
energy to release the water

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that's coating the
grains of the soil.

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Most of that water will get
released into space, and that's

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the signature that LADEE detects
with its instrument from its

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orbit.

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LADEE observed water being
released from within the moon,

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but the micrometeoroids
impacting the moon's surface

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have a more
exotic origin: comets.

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When Earth passes through
the leftover debris trail of a

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comet, small particles of
rock and dust burn up in our

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atmosphere,
creating a meteor shower.

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On the moon, these
micrometeoroids impact the

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surface, releasing water at the
same time that meteor showers

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are occuring on Earth.

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By analyzing the data
returned by the neutral mass

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spectrometer, we found that the
intensity and the frequencies of

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the fluctuations of signals
from the water to be perfectly

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correlated with
known meteor streams.

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For example, we were able to
detect a big spike of water

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during the Geminid meteor shower
that occurred in December of

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2013.

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Knowing how much water is
available at the moon's mid

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latitudes is important
for future exploration.

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LADEE's observations show
that beneath three inches of dry

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lunar soil is a wet
layer ten feet deep.

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But on the moon,
"wet" is a relative term.

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The concentration of water in
the wet layer is about 200-500

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part per million per weight.

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 So, to fill an eight-ounce
bottle with lunar water, you

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would need to squeeze water
out of about one to two thousand

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pounds of lunar soil.

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So, while the wet surface is
wet, it's drier than you think.

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The search for water on the moon
spans five decades, and is of

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great interest to
future exploration.

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Thanks to LADEE, we now know
that trace amounts of water are

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widely distributed across the
lunar surface, improving our

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understanding the moon's
geologic past and its continued

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evolution.

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[music]