[meteorite-list] Moon Storms

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Dec 7 17:08:57 2005
Message-ID: <200512072207.jB7M7On23561_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2005/07dec_moonstorms.htm

Moon Storms
NASA Science News
December 7, 2005

An old Apollo experiment is telling researchers something new and
surprising about the moon.


December 7, 2005: Every lunar morning, when the sun first peeks over the
dusty soil of the moon after two weeks of frigid lunar night, a strange
storm stirs the surface.

The next time you see the moon, trace your finger along the terminator,
the dividing line between lunar night and day. That's where the storm
is. It's a long and skinny dust storm, stretching all the way from the
north pole to the south pole, swirling across the surface, following the
terminator as sunrise ceaselessly sweeps around the moon.

Never heard of it? Few have. But scientists are increasingly confident
that the storm is real.

The evidence comes from an old Apollo experiment called LEAM, short for
Lunar Ejecta and Meteorites. "Apollo 17 astronauts installed LEAM on the
moon in 1972," explains Timothy Stubbs of the Solar System Exploration
Division at NASA's Goddard Space Flight Center. "It was designed to look
for dust kicked up by small meteoroids hitting the moon's surface."

Billions of years ago, meteoroids hit the moon almost constantly,
pulverizing rocks and coating the moon's surface with their dusty
debris. Indeed, this is the reason why the moon is so dusty. Today these
impacts happen less often, but they still happen.

Apollo-era scientists wanted to know, how much dust is ejected by daily
impacts? And what are the properties of that dust? LEAM was to answer
these questions using three sensors that could record the speed, energy,
and direction of tiny particles: one each pointing up, east, and west.

LEAM's three-decade-old data are so intriguing, they're now being
reexamined by several independent groups of NASA and university
scientists. Gary Olhoeft, professor of geophysics at the Colorado School
of Mines in Golden, is one of them:

"To everyone's surprise," says Olhoeft, "LEAM saw a large number of
particles every morning, mostly coming from the east or west--rather
than above or below--and mostly slower than speeds expected for lunar
ejecta."

What could cause this? Stubbs has an idea: "The dayside of the moon is
positively charged; the nightside is negatively charged." At the
interface between night and day, he explains, "electrostatically charged
dust would be pushed across the terminator sideways," by horizontal
electric fields.

Even more surprising, Olhoeft continues, a few hours after every lunar
sunrise, the experiment's temperature rocketed so high--near that of
boiling water--that "LEAM had to be turned off because it was overheating."

Those strange observations could mean that "electrically-charged
moondust was sticking to LEAM, darkening its surface so the experiment
package absorbed rather than reflected sunlight," speculates Olhoeft.

But nobody knows for sure. LEAM operated for a very short time: only 620
hours of data were gathered during the icy lunar night and a mere 150
hours of data from the blazing lunar day before its sensors were turned
off and the Apollo program ended.

Astronauts may have seen the storms, too. While orbiting the Moon, the
crews of Apollo 8, 10, 12, and 17 sketched "bands" or "twilight rays"
where sunlight was apparently filtering through dust above the moon's
surface. This happened before each lunar sunrise and just after each
lunar sunset. NASA's Surveyor spacecraft also photographed twilight
"horizon glows," much like what the astronauts saw.

It's even possible that these storms have been spotted from Earth: For
centuries, there have been reports of strange glowing lights on the
moon, known as "lunar transient phenomena" or LTPs. Some LTPs have been
observed as momentary flashes--now generally accepted to be visible
evidence of meteoroids impacting the lunar surface. But others have
appeared as amorphous reddish or whitish glows or even as dusky hazy
regions that change shape or disappear over seconds or minutes. Early
explanations, never satisfactory, ranged from volcanic gases to
observers' overactive imaginations (including visiting extraterrestrials).

Now a new scientific explanation is gaining traction. "It may be that
LTPs are caused by sunlight reflecting off rising plumes of
electrostatically lofted lunar dust," Olhoeft suggests.

All this matters to NASA because, by 2018 or so, astronauts are
returning to the Moon. Unlike Apollo astronauts, who never experienced
lunar sunrise, the next explorers are going to establish a permanent
outpost. They'll be there in the morning when the storm sweeps by.

The wall of dust, if it exists, might be diaphanous, invisible,
harmless. Or it could be a real problem, clogging spacesuits, coating
surfaces and causing hardware to overheat.

Which will it be? Says Stubbs, "we've still got a lot to learn about the
Moon."
Received on Wed 07 Dec 2005 05:07:23 PM PST