Meteorites
For some time now, scientists have been traveling by snowmobile along
the margins of the polar plateau west of the Transantarctic Mountains.
They are searching for meteorites--material that has impacted the
Earth from outer space. Prior to 1969, however, when nine meteorites
were found almost by accident, by the Japanese in the Yamato Mountains
near their Syowa Base, only six meteorites had been found in Antarctica
the first in 1912. In fact, prior to 1969, only about 2100 distinct
(individual, not fragments) meteorites were known worldwide, with
only five to ten new ones being recovered annually from the rest of
the Earth.
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Space Rocks
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Meteorites are a major source of information
about the early history of our solar system.
Most of our knowledge about meteorites
comes from analysis of those found in Antarctica, which acts
as a huge meteorite collector and preserver.
The first Antarctic meteorite was found
by Australians in 1912, but serious collecting did not begin
until 1969.
Since then, more than 10,000 have been
discovered, mainly by Japanese and US scientists.
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Antarctica
is a unique collecting ground for the recovery of large numbers
of meteorites. It has been determined that meteorites striking the
vast ice sheet are better preserved than anywhere else in the world,
through their burial in the ice for periods ranging from 1000 to
700,000 years (dated by isotope measurements). This is relatively
old when considering the 200 year old age identified for meteorites
found in more humid and less protected regions of the Earth. The
meteorites are believed to move downward within the ice, following
its flow lines toward the continental margins, where they are either
discharged unnoticed into the sea or are captured in ice where they
stagnate against a resistant mountain barrier, There the flow path
in the ice brings them to the surface, where they are now being
found in large numbers.
Today, there are consortiums
of many nations whose members are busy searching the ice
sheet and picking up these samples from outer space.
Most of the fun may be
in the finding, but the science is taken seriously to the
point of keeping the meteorites frozen until they can be
returned to a "clean lab," where they are treated with the
same care that was given to the samples returned from the
moon.
Some of them have been
found to be unlike any others found elsewhere on earth.
Not entirely without
reason, the collectors have taken to referring to a find
as "a poor man's space probe."
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Among the most
unexpected finds was a meteorite fragment whose mineral content identified
it as coming from the Moon, presumably a result of "splatter" created
by the impact on the lunar surface of a large asteroid. For such a
rock to travel to the Earth from the Moon would require an escape
velocity from the Moon accelerated to about 8,750 kilometers per hour.
Even more incredible is the meteorite fragments found from Mars--the
escape velocity from that planet would have to be about 18,000 kilometers
per hour. These specimens are at the center of the controversy about
possible evidence of microbial life on early Mars.
Meteorite studies
are a significant part of space science because the specimens include
the oldest materials of the Solar System available for research.
 They
provide identifiable records of certain solar and galactic effects,
and they yield data that are otherwise not obtainable--about the
origin, evolution, and composition of the Sun, the Earth, and other
planets, satellites, and asteroids. The techniques and ideas developed
in the collection, study, and preservation of meteorite specimens
are transferable to the studies of lunar samples, and have thereby
yielded large amounts of information about the Moon and Sun, and
the Solar System.
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Why Are
So Many Meteorites Found in Antarctica?
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They are easily seen against the ice.
They are quickly covered by snow and eventually
frozen solidly into the icepack, protecting them from rusting,
weathering and corroding.
The ice sheet both transports and concentrates
the meteorites as it slips off the plateaus and churns against
the mountains.
The meteorites are generally found in
the 'blue ice' areas of Antarctica, which are expanses of
old ice kept free of snow by constant winds.
Areas of sublimating (evaporating) ice
allow the meteorites to gradually 'rise' to the surface.
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