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The Search for Antarctic Meteorites
Background
The National Science Foundation (NSF), through its
Office of Polar Programs (OPP), is the lead agency
of a consortium of U.S. government agencies that searches
for, characterizes, and makes available to researchers
worldwide, meteorites that have landed in Antarctica.
NSF, through the U.S. Antarctic Program, coordinates
almost all U.S. scientific research in the Antarctic.
NSF is an independent federal agency and is the only
federal agency whose mission covers research in all
fields of science and engineering.
Organization
The Antarctic meteorite program is a collaborative
effort of NSF, NASA, and the Smithsonian Institution.
NSF, through the Antarctic Search for Meteorites (ANSMET)
Program, supports the collection of meteorites in
Antarctica. ANSMET is presently supported by a grant
to Case Western Reserve University in Cleveland, Ohio.
NASA and the Smithsonian Institution provide for the
classification, curation, and distribution of Antarctic
meteorites. All three agencies sponsor research on
these specimens.
ANSMET's goals
ANSMET's primary goal is to recover an unbiased and
uncontaminated sample of meteorites each year. The
program aims to recover a sufficiently large number
of meteorites each Antarctic research season to make
it likely that a few unusual or unique specimens will
be collected.
Since 1976, ANSMET has recovered more than 10,000 specimens
from meteorite stranding surfaces in the Transantarctic
mountains. These specimens serve as one of the most
reliable, continuous sources of new, non-microscopic
extraterrestrial material. The study of Antarctic
meteorites has greatly extended knowledge of the materials
and conditions in the primeval nebula from which our
solar system was born; revealed the complex and exotic
geologic nature of asteroids; and proved that some
specimens recovered from Antarctica represent planetary
materials from the Moon and Mars.
Why Antarctica?
Antarctica is one of the best places on Earth to search
for meteorites for two reasons:
- Although meteorites fall randomly all over the
globe, it is much easier to find a meteorite if
the background material it is resting on is light
colored and plain, and there are few terrestrial
rocks to complicate the search. Both of these
factors make the East Antarctic ice sheet an excellent
place for finding meteorites.
- Along the margins of the ice sheet, ice flow is
sometimes blocked by mountains and other obstructions,
exposing slow moving or stagnant ice to the fierce
"katabatic" winds that roar down the ice cap from
the South Pole to the ocean. These winds, in turn,
scour away the ice, leaving behind a deposit of
meteorites representing those that were sprinkled
throughout the volume of ice lost to the wind.
When such a process continues for tens or hundreds
of thousands of years, as is the case in Antarctica,
the concentration of meteorites can be spectacular.
There are indications that some of the surfaces
where meteorites have been found may have been
active for millions of years
Finding meteorites
Meteorite collection follows a system developed over
the past 25 years that allows for the most efficient
search over a wide area with the minimum of logistical
support.
Six-person recovery teams leave from McMurdo Station,
the main U.S. research station in Antarctica, for
remote field sites for a period of 5-7 weeks. The
teams are self-sufficient in terms of equipment, fuel,
food, and other materials, and are housed in tents.
They generally are flown into the field aboard ski-
equipped aircraft, such as Twin Otters or LC-130’s.
From the landing site, the field team moves to a meteorite-stranding
surface, where systematic searching begins. To search,
the field team, on snowmobiles, forms a line roughly
30 meters (100 feet) apart and slowly drives across
the icefield, scanning for specimens. The transects
are arranged to provide significant overlap making
it less likely that specimens will be missed and minimizing
exposure to uncomfortable crosswinds which affect
visibility.
Many meteorite-stranding surfaces require several years
to search because of their size. Training helps ensure
consistent recovery methods from year to year. This,
in turn, ensures that the sum of collected meteorites
from a given icefield constitute an unbiased sample
of the meteorites.
Once a sample is located, it is assigned an identification
number; its position is established using the Global
Positioning System (GPS) and notes are made of its
size, possible classification, and any distinguishing
features such as shape or color. The sample is then
collected in a sterile Teflon bag, with care being
taken to avoid contact with any mechanical or biological
materials. While the field season is in progress,
these samples are carefully inventoried and kept frozen.
When the team returns to McMurdo, the meteorites are
transferred to special shipping containers and sent,
still frozen, to the Antarctic Meteorite Curation
Facility at NASA's Johnson Space Center (JSC) in Houston,
Texas. There the meteorites are carefully removed
from their sealed bags, dried to remove any attached
snow or ice, and stored under cleanroom conditions.
How are meteorites distributed for research use
After each new specimen arrives at JSC, and has been
freeze-dried to remove any ice or snow, technicians
there carefully examine the meteorite both macro-
and microscopically. Small chips are then broken off
for initial classification, by curatorial staff at
both JSC and at the Smithsonian Institution.
The product of these initial examinations is a short
written description, which is subsequently published
in the Antarctic Meteorite Newsletter that is distributed
to researchers and facilities around the globe twice
each year. This newsletter invites interested researchers
to request samples by submitting requests to the Curator
of Meteorites at JSC. Sample requests that fall outside
of established curatorial policies for distribution
are considered by the Meteorite Working Group, an
expert peer group established to provide technical
advice about sample handling and allocation.
For more information about the ANSMET Program, see:
http://www.cwru.edu/affil/ansmet/
For NASA's Johnson Space Center's meteorite program,
see: http://wwwcurator.jsc.nasa.gov/curator/antmet/program.htm
For NSF's most recent news release on ALH84001, an
Antarctic meteorite of Martian origin, see: http://www.nsf.gov/od/lpa/news/press/00/pr0096.htm
Broadcasters
B-roll and sound bites from NSF’s Scott Borg are available
on Betacam SP, contact NSF’s Dena Headlee, (703) 292-8070/dheadlee@nsf.gov
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