[meteorite-list] Magnetic Moondust

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Apr 5 16:23:25 2006
Message-ID: <200604051810.k35IAcs20383_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2006/04apr_magneticmoondust.htm

Magnetic Moondust
NASA Science News
April 4, 2006

April 4, 2006: Thirty-plus years ago on the moon, Apollo astronauts made
an important discovery: Moondust can be a major nuisance. The fine
powdery grit was everywhere and had a curious way of getting into
things. Moondust plugged bolt holes, fouled tools, coated astronauts'
visors and abraded their gloves. Very often while working on the
surface, they had to stop what they were doing to clean their cameras
and equipment using large--and mostly ineffective--brushes.

Dealing with "the dust problem" is going to be a priority for the next
generation of NASA explorers. But how? Professor Larry Taylor, director
of the Planetary Geosciences Institute at the University of Tennessee,
believes he has an answer: "Magnets."

The idea came to him in the year 2000. Taylor was in his lab studying a
moondust sample from the Apollo 17 mission and, curious to see what
would happen, he ran a magnet through the dust. To his surprise, "all of
the little grains jumped up and stuck to the magnet."

"I didn't appreciate what I had discovered," recalls Taylor, "until I
was explaining it to Apollo 17 astronaut Jack Schmitt one day in my
office, and he said, 'Gads, just think what we could have done with a
brush with a magnet attached!'"

"Only the finest grains (< 20 microns) respond completely to the
magnet," notes Taylor, but that's okay because the finest dust was often
the most troublesome. Fine grains were more likely to penetrate seals at
the joints of spacesuits and around the lids of "pristine" sample
containers. And when astronauts tramped into the Lunar Module wearing
their dusty boots, the finest grains billowed into the air where they
could be inhaled. This gave at least one astronaut (Schmitt) a case of
"moondust hay fever."

Taylor has since designed a prototype air filter with permanent magnets
inside. "When the filter gets dirty, you pull the magnets out, and the
dust falls into a box." A later design with electromagnets works more
efficiently: "You pull the plug on the electromagnet, tap it, and the
dust rains down into a container." He's now working on a prototype
design for a "dust brush" using permanent magnets.

Earth dust is not magnetic, so why should moondust be?

"Moondust is strange stuff," explains Taylor. "Each little grain of
moondust is coated with a layer of glass only a few hundred nanometers
thick (1/100th the diameter of a human hair)." Taylor and colleagues
have examined the coating through a microscope and found "millions of
tiny specks of iron suspended in the glass like stars in the sky."
Those iron specks are the source of the magnetism.

Researchers believe the glass is a by-product of bombardment. Tiny
micrometeorites hit the surface of the moon, generating temperatures
hotter than 2,000??C, literally the surface temperature of red stars.
Such extreme heat vaporizes molecules in the melted soil. "The vapors
consist of compounds such as FeO and SiO2," says Taylor. If the
temperature is high enough, the molecules split into their atomic
components: Si, Fe, O and so on. Later, when the vapors cool, the atoms
recombine and condense on grains of moondust, depositing a layer of
silicon dioxide (SiO2) glass peppered with tiny nuggets of pure iron (Fe).

A thin coating of iron isn't enough to make sand- or gravel-sized
particles noticeably magnetic, any more than spraying a thin coating of
iron on a heavy basketball would make it stick to a magnet, says Taylor.
But a thin coating is plenty for particles smaller than about 20
microns. They have so little mass compared to their surface area,
they're easily lifted by Taylor's magnets.

Magnets aren't the only way to deal with moondust. NASA is considering a
whole suite of options from airlocks to vacuum cleaners. But, if Taylor
is right, magnets will prove important, and astronauts won't find
moondust so troublesome the next time around.
Received on Wed 05 Apr 2006 02:10:37 PM PDT