Water Released from Moon: Director’s Cut
Transcript
FADE IN
NARRATOR:
Compared to Earth, the moon
appears to be perfectly dry and airless, but in fact it possesses an extremely
sparse atmosphere, barely thicker than a vacuum.
From late 2013 to early 2014,
a NASA mission called LADEE explored the lunar atmosphere and dust environment.
Now, LADEE’s observations have led to a new discovery about the moon’s water.
BENNA:
During the initial
exploration of the moon, and the analysis of all the returned samples from the
Apollo and the Luna missions, we thought that the surface of the moon was dry.
But more recent missions,
like Lunar Prospector, LCROSS, and Lunar Reconnaissance Orbiter, have not only
shown that the surface of the moon has a global hydration, but there are
actually high concentrations of ice water in the permanently shadowed regions
of the lunar poles.
NARRATOR:
In the decades following the
Apollo program, a series of robotic explorers revealed tantalizing hints of
water on the moon, challenging the conclusion that the moon was dry.
The first definitive
discovery of water was made in 2008 by the Indian mission Chandrayaan-1, which
detected hydroxyl molecules spread across the lunar surface and concentrated at
the poles. The following year, NASA’s LCROSS mission deliberately impacted part
of its launch vehicle into the southern crater Cabeus, ejecting a plume that
contained water ice.
These discoveries showed that
the moon harbors water, and that the highest concentrations occur within
darkened craters at the poles. But questions remained about the abundance of
water at the moon’s mid latitudes.
Now, data from LADEE are beginning provide answers.
BENNA:
What we discovered is that
the surface releases its water when the moon is bombarded by micrometeoroids.
This is especially noticeable during meteor showers. What we also found is that
the surface that’s releasing the water is being protected by a layer, a few
centimeters of dry soil that can only be breached by large micrometeoroids.
When micrometeoroids impact
the surface of the moon, most of the material in the crater is vaporized. There
is also a shock wave that propagates outward. That shock wave carries enough
energy to release the water that’s coating the grains of the soil. Most of that
water will get released into space, and that’s the signature that LADEE detects
with its instrument from its orbit.
NARRATOR:
LADEE observed water being
released from within the moon, but the micrometeoroids impacting the moon’s
surface have a more exotic origin: comets.
When Earth passes through the
leftover debris trail of a comet, small particles of rock and dust burn up in
our atmosphere, creating a meteor shower.
On the moon, these
micrometeoroids impact the surface, releasing water at the same time that meteor
showers are occuring on Earth.
BENNA:
By analyzing the data
returned by the neutral mass spectrometer, we found that the intensity and the
frequencies of the fluctuations of signals from the water to be perfectly
correlated with known meteor streams. For example, we were able to detect a big
spike of water during the Geminid meteor shower that occurred in December of
2013.
NARRATOR:
Knowing how much water is available
at the moon’s mid latitudes is important for future exploration. LADEE’s
observations show that beneath three inches of dry lunar soil is a wet layer
ten feet deep. But on the moon, “wet” is a relative term.
BENNA:
The concentration of water in
the wet layer is about 200-500 part per million per weight. So, to fill an eight-ounce bottle with lunar water, you
would need to squeeze water out of about one to two thousand pounds of lunar
soil. So, while the wet surface is wet,
it’s drier than you think.
NARRATOR:
The search for water on the
moon spans five decades, and is of great interest to future exploration. Thanks
to LADEE, we now know that trace amounts of water are widely distributed across
the lunar surface, improving our understanding the moon’s geologic past and its
continued evolution.
FADE TO BLACK.