![](img/lunar-soil-micro.jpg)
NASA
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The soil on the moon
looks like it's wet, or is made of plaster or something. Look at how
sharp the footprints and other impressions are?
Several powdered substances on earth exhibit this behavior.
Anything finely powdered, such as cornstarch or flour, will clump when
packed. Even earth dust, if sufficiently fine, will receive a print
quite well even when dry.
The secret is in the microscopic structure of the individual soil
particles, shown at right. On earth most soil particles rub against
each other as they are acted upon by wind and water. This rubs off
the rough edges. But lunar soil has no wind or water to erode it at
the microscopic level, and so it retains those sharp edges that allow
each particle to "catch" its neighbor and display the remarkable
cohesion we can observe.
How could there be soil
without erosive forces like wind and rain?
In Stanley Kubrik's 2001: A Space Odyssey the lunar
mountains appear sharp and highly detailed. People were surprised to
see more rounded features.
As a matter of fact, wind and water are not the only forces that
cause erosion. The lunar soil is produced chiefly by the
pulverization of the rocky surface by millions of years' worth of
micrometeroids. And larger ones as well. When a large meteor strikes
the lunar surface, a blanket of pulverized material called "ejecta" is
thrown for miles around the crater.
The moon was also once seismically active. The "seas" are in fact
ancient lava flows. The moon is tidally locked, which is a fancy way
of saying that the same side always faces earth. The process of tidal
locking exerts considerable forces on the lunar surface which can warp
and distort features.
Harvard geologist Arthur Gold maintained the lunar soil would be
several feet thick and that the Apollo astronauts would sink into it
over their heads. Fortunately he was wrong about that, but the lunar
soil is in fact several feet thick. But only the top inch or so is
loose. The rest is very densely packed. But the top scientists at
the time knew there would be particulate matter on the lunar surface,
and they knew why.
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