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MIACAntarctic meteorites |
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MIACAntarctic meteorites |
Allan Hills, in Eastern Antarctica, forms a barrier to the flow of ice
into the Ross Sea. This is the region where an American party first searched
in 1976 following spectacular earlier discoveries by the Japanese in the
Yamato (Queen Fabiola) Mountain area on the other side of the continent.
In the Allan Hills area, rocks actually protrude above the ice to form
the barrier, but in other areas it has been found that buried topography
can cause an upward movement of ice, leading to ablation and the exposure
of meteorites. American teams have now located meteorites at more than
20 localities in Antarctica. Most of these are situated to the west or
south of the Ross Sea and Ross Ice Shelf. (Courtsey Dr. Ursual Marvin,
Smithsonian Astrophysical Laboratory, Cambridge, Ma., U.S.A.)
This slide shows the mechanism of concentration of meteorites in Antarctica
originally proposed by Kezio Yanai of the Japanese National Institute of
Polar Research in Tokyo. Meteorites falling on the ice cap in regions of
substantial accumulation are gradually buried deeper in the ice and are
carried with it as it flows toward lower ground. Although much of the ice
(and the meteorites it contains) ends up in the sea, some of it comes up
against natural barriers, such as a range of hills or mountains. Here the
ice is forced upward. Ablation from katabatic winds continually removes
ice from the upper surface and leaves the meteorites it contained, exhumed
on the surface. Such dense, compact ice with no snow cover is a distinct
pale blue colour. (Courtesy Dr. Ursula Marvin, Smithsonian Astrophysical
Laboratory, Cambridge, Ma., U.S.A)
This slide shows a small meteorite still embedded in Antarctica blue ice.
Note that an identification number ('439') has been painted on the ice
before it was photographed. The meteorite is then chipped out of the ice
and taken in an inert atmosphere and still frozen to a facility at the
Johnson Space Centre in Houston, where it is finally stored under a program
run jointly by NASA and the Smithsonian. 'Terrestrial' isotopic ages of
these Antarctic meteorites offer a means of dating the ice sheet. Meteorites
recovered from the ice have been referred to as 'fossil' meteorites and
distinguished as a group from those found elsewhere on Earth. (Courtesy
Dr. Ursula Marvin, Smithsonian Astrophysical Laboratory, Cambridge, Ma.,
U.S.A.)
More information on Antarctic meteorites is available from Johnson Space Center