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Re: Lunar Sodium Tail Discovered


-----Original Message-----
From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
To: meteorite-list@meteoritecentral.com
<meteorite-list@meteoritecentral.com>
Date: Thursday, June 03, 1999 10:43 AM
Subject: Lunar Sodium Tail Discovered


The very thin lunar atmosphere also receives contributions from volcanic
outgassing.  The excess of lunar radon and polonium being emitted from the
Aristarchus Plateau, and their varying ratios from day to day demonstrate
this.        D. Futrell


>Boston University
>
>Contact: Shauna LaFauci, 617/353-2399, slafauci@bu.edu
>
>For Immediate Release: June 2, 1999
>
>BOSTON UNIVERSITY CENTER FOR SPACE PHYSICS DISCOVERS LUNAR SODIUM TAIL
>
>Boston, Mass. -- Boston University astronomers announced today the
>discovery of an enormous tail of sodium gas stretching to great distances
>from the moon. The observations were made at the McDonald Observatory in
>Fort Davis, Texas, on nights following the Leonid meteor shower of November
>1998. The tail of sodium gas was seen to distances of at least 500,000
miles
>from the moon, changing its appearances over three consecutive nights.
These
>results were presented on Tuesday, June 1st, at the Annual Spring Meeting
of
>the American Geophysical Union (AGU) in Boston. Complete papers will appear
>in the AGU journal Geophysical Research Letters in its June 15th edition.
>
>Since the days of NASA's Apollo Program of lunar, scientists have known
that
>the moon has a very thin atmosphere. "It is one continuously being produced
>by evaporation of surface materials, and then continuously being lost by
>escape or impact back onto the surface," said Michael Mendillo, professor
of
>astronomy. Such processes act daily, and so while there is always some
>atmosphere present, the various gases are being cycled through it. It is a
>"transient atmosphere" similar to the ones found in comets.
>
>Ten years ago, groundbased telescopes revealed that sodium gas (Na) was in
>the lunar atmosphere, an element that can be used to trace the shape and
>behavior of such a thin atmosphere. Sodium reflects sunlight very
>efficiently and so has become a standard way for space scientists to study
>gases that are otherwise difficult to see.
>
>"There are less than 50 atoms of sodium per cubic centimeter in the
>atmosphere just above the surface of the moon," says Jeffrey Baumgardner,
>Senior Research Associate in the University's Center for Space Physics.
"But
>the most modern camera systems built in our lab can photograph such a thin
>environment out to distances that are several times the radius of the
moon,"
>Baumgardner added. In contrast to the tenuousness the moon's atmosphere --
>only 50 atoms per cubic centimeter -- there are 10**19 molecules per cubic
>centimeters in earth's atmosphere at the surface.
>
>During the November observations, the BU team pointed their sensitive
camera
>in the opposite direction from the moon and recorded, just by chance,
images
>of the tail in an otherwise moonless sky. "At the time of the Leonid meteor
>shower on November 17, 1998, the moon was in 'new' phase, impossible to see
>at its location between the Earth and the Sun," described Dr. Steven Smith,
>research associate in the center for space physics. "Our team was operating
>on the nightside of the earth, essentially looking away from the sun and
>moon, searching for meteor effects in our atmosphere." After one night of
>uneventful observations, on November 18th our imaging system detected a
>small patch of sodium emission in the dark skies above west Texas. "It grew
>to be larger and brighter on November 19th, and then faded slightly on
>November 20th," Smith said.
>
>The BU team considered several theories that could explain these unusual
>features, ruling out a comet, the impact of Leonid meteors upon dust in the
>solar system, and even possible instrumentation problems. Dr. Jody Wilson,
>research associate in the BU space physics group suggested that the
>mysterious sodium gas might come from the moon, and set out to model it
>using computer simulation and visualization techniques. "We found out that
>when the moon is new, it takes two days or so for Sodium atoms leaving the
>surface to reach the vicinity of the earth. They are pushed away from the
>moon by the pressure of sunlight and, as they sweep past us, the earth's
>gravity pulls on them, focusing them into a long narrow tail," Wilson
>explained.
>
>"The pieces of the puzzle fit together rather well," Mendillo added. "While
>some of the Leonid meteors burned up in their streaks through the earth's
>atmosphere on the night of November 17th -- producing spectacular showers
>in some locations -- others crashed into the moon's dusty soil liberating
>sodium gas. These atoms, speeding away from the earth-moon system, were
>then captured in photographs from our instrument in Texas several days
>later, looking down the length of the tail."
>
>"If it were bright enough for the human eye to see, perhaps a thousand
times
>brighter," Baumgardner added, "it would be a glowing orange cloud
dominating
>the nighttime, moonless sky."
>
>In trying to determine if this comet-like appearance of the moon occurred
>only on nights following a strong meteor shower, as happened with the
>Leonids, the BU team examined some earlier data taken at their site in
>Texas. During the previous August, similar observations were made,
>fortuitously on the nights following the new moon of August 21, 1998. "It
>was there," Dr. Smith said, "several times fainter, but with the same
shapes
>over the same three nights spanning the new moon, just as occurred in
>November."
>
>Taken together, the August observations without meteors and the November
>observations with meteors imply that the daily flux of micrometeors that
>strikes the moon's surface creates an extended tail at all times; it was
>just so enhanced during the strong Leonid storm that it was observed rather
>easily.
>
>"What we do not know yet is whether the entire atmosphere of the moon is
>produced by meteors, or just the small component of fast sodium atoms that
>can escape from it," Mendillo said.
>
>For visual information http://vega.bu.edu/moontail .
>
>
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