Antarctica: A Meteorite Storehouse
In a recent Geotimes article, Michael Lipschutz makes the observation that meteorites resulting from between 1,200 and 3,500 impacts have been found in Antarctica, while only a little more than 2,600 are known from the rest of the world. (The distinction must be made here that he is referring to distinct meteorite impacts, each of which may produce many individual meteoritic fragments.) More than 7,000 fragments have now been collected from Antarctica. Naturally, the question arises: why are there so many in this single small continent?
The answer seems to lie partly in the ease with which they are seen against the ice. On regular "earthy" terrain, a meteoritic fragment would be easily lost against the background of other, equally nondescript pebbles.
But there is more to it than that. Meteorites that fall on Antarctica are quickly covered by snow and eventually frozen solidly into the icepack. This is an important first step, in that it protects the sample for many thousands of years from rusting, weathering and corroding. Eventually, as the ice sheet flows and thickens below, layers are "rotated" back to the surface. Here, ablation of the old, blue ice occurs, gradually exposing whatever had been entrapped in it. (Ablation is a term used to describe all the erosive processes that reduce a glacier. In the Antarctic, the winds and sublimation of the ice--evaporation--are important factors.)
In Antarctica, there is an added twist. The ice sheet is perpetually trying to slip off the plateaus and flow into lower areas of the continent or into the ocean. In so doing, it plays an important role in transporting and concentrating the samples that it contains.
Most Antarctic meteorites are found at the surface in the old ice just "upstream" from mountain barriers. The ice has transported them that far, but in churning over as it tries to clear a mountain, it has brought the meteorites to the surface, ablated in the process, and left the passengers stranded there.
As a result, the largest concentrations of meteorites in Antarctica are found flanking the Transantarctic Mountains, which cross the continent along a line roughly drawn from New Zealand through the South Pole. This greatly limits the most favorable search areas.
The existence of these concentrations was not known in 1912 when the first Antarctic meteorite was found near the coast by Australian explorers (had they not found it, in a few hundred years that sample probably would have been on the floor of the ocean). Today, there are consortiums of many nations whose members are happily rambling about the ice sheet on snow machines, 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."
