The
moon has never had all that much. It doesn't have atmosphere, it
doesn't have water and it sure doesn't have life. What it does have
though is dirt -- lots and lots of dirt -- and it's some of the coolest
stuff you ever saw. Now it's gotten cooler still, thanks to the
discovery this week of a wholly unexpected ingredient stirred into the
lunar mix.
Even before astronauts landed on the moon, they knew the soil would
be something special. With no atmosphere to intercept incoming
meteorites and micrometeorites, the lunar regolith -- or surface
covering -- would have been subjected to a 4.5 billion year bombardment
that would have produced a layer of dust far finer than confectioner's
sugar. That dust, the Apollo crewmen found when they went out to play in
it, did some strange things: it rose above the surface when disturbed
and hung there far longer than could be explained by the moon's weak
gravity; it crept deep into the weave and cracks of virtually anything
it touched and clung there as if adhesively attached. What's more, it
was filled with exquisitely fine green and orange glass beads -- the
products of the superheated melting and cooling that followed impacts.
(PHOTOS: 'Ring of Fire' Solar Eclipse Dazzles Spectators Around the Earth)
When the astronauts brought their samples home, the geologists in
Houston discovered even more. The soil was unusually chemically reactive
-- not something that was expected from a scrap of a world that was
supposed to be largely inert. And it did a lousy job of conducting heat.
The surface of the moon on the sunlit side might be close to the
boiling point of water, but just a few feet down it would be far below
freezing.
For 40 years, geologists struggled to understand just what gave lunar
soil these pixie dust properties, but geologist Marek Zbik of
Queensland University of Technology in Brisbane, Australia may finally
have cracked it. The answer: nanoparticles -- vanishingly tiny flecks of
mass, some no bigger than molecules, that have all the odd qualities of
moon dust, and more.
Zbik made his discovery thanks to an instrument known as a
synchrotron-based nano tomograph -- a hunk of hardware that didn't
remotely exist when the Apollo crews splashed down. Nano tomographs work
by bombarding nano particles with x-rays to produce 3-D images of
structures that otherwise would be far too tiny to see -- or at least to
see well. When Zbik got some lunar soil and a nano tomograph in the
same room together, he knew that the first thing he wanted to look at
were the infinitesimal glass bubbles scattered through the lunar
material.
(SPECIAL: The 40th Anniversary of the Moon Landing)
The bubbles are formed the same way the larger glass beads are formed
-- in the fiery heat of meteorite collisions -- but their exotic
origins notwithstanding, they still ought to be built like any other
bubble. That means they ought to be filled with some kind of gas. That,
however, wasn't the case. "Instead of gas or vapor," says Zbik, "the
lunar bubbles were filled with a highly porous network of alien-looking
glassy particles that span the bubbles' interior."
Alien-looking maybe, but Zbik quickly recognized them as nano
particles -- and that would explain a lot. Nano particles can become
electro-statically charged, which would impart the same property to the
soil, perfectly accounting for its tendency to float. They have low
thermal conductivity, explaining why the lunar subsoil can get so cold
so close to the surface. They are chemically active, and they are also
electrically sticky, meaning that when the soil got on an astronaut's
pressure suit or into the joints of his lunar tools it would be all but
impossible to brush away.
What was not immediately evident was why the nano particles had a
chance to interact with the soil at all. The ones that were spotted by
the tomograph, after all, were sealed inside the bubbles like a figurine
in a snow globe. Something would have to be breaking those globes, and
Zbik reckons it was the same thing that created them in the first place:
collisions.
(MORE: Lunar Liquid: More Water than Ever Found on the Surface of the Moon)
"It appears that the nano particles are formed inside bubbles of
molten rocks when meteorites hit the lunar surface," he says. "Then they
are released when the glass bubbles are pulverized by the consequent
bombardment of [more] meteorites. This continuous pulverizing ... and
constant mixing develop a type of soil which is unknown on Earth."
There's more than just abstruse soil science in all this. Nano particles have long been the
it
material for engineers working on new computer hardware, medical
equipment, drug-delivery systems, even fabric. The better we understand
their origins and properties, the better we can manipulate them. What's
more, if we ever hope to establish a long-term human presence on the
moon, the tendency of the soil to cling to surfaces and, ultimately, to
wear them away is a problem that will have to be addressed. Studying the
dust now can provide solutions for later.
That, however, is for another time. For now it's enough just to
appreciate the elegance of both the new discovery and the moon itself.
Four decades after we last dropped by for a visit, our little satellite
is still surprising us.
LIST: Top 10 Things You Didn't Know About The Moon
SPECIAL: The Moon Race
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