Meteorite hunting in Antarctica

It's a haven for scientists studying the Earth's climate and ecological conditions; it's a rich mineral source and a home to penguins and seals, but at first glance it's hard to comprehend what Antarctica and outer space have in common.

For the organisations behind the North American Antarctic Search for Meteorite (ANSMET) Program however, the answer's simple: it's one of the Earth's best and most reliable sources of new, non-microscopic extraterrestrial material.

The ANSMET Program is a collaborative effort of US National Science Foundation's (NSF) Antarctica Program, NASA and the Smithsonian Institution. The Program's primary aim is to search for, characterise and make available to researchers worldwide the unbiased and uncontaminated samples of meteorites recovered from Antarctica.

The NSF says meteorites collected from Antarctica have helped to extend knowledge of the solar system, revealed the geological nature of asteroids and have even contributed to unravelling planetary conditions on the moon and Mars.

More than 10,000 meteorite specimens have been recovered in Antarctica since annual meteorite expeditions began in 1976. According to the NSF, the region is one of the best places on Earth to search for meteorites for two reasons. Firstly, while meteorites fall all over the globe they are much easier to spot if the background material is light-coloured and plain - like ice. Secondly, there are few terrestrial rocks along the Antarctica plain to complicate the search.

"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," the NSF says.

"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."

Scott Borg, program director of the NSF's Antarctic Geology and Geophysics Program, says the meteorite expeditions are undertaken in a "low tech" way, with the field party crossing the chosen area on snowmobile or on foot.

Six-person recovery teams fly out aboard ski-equipped aircraft from McMurdo Station, the main US research station in Antarctica, for remote field sites where they spend a period of five to seven weeks. From the landing site, the field team moves to a meteorite-stranding surface where systematic searching begins. To search, the field team members form a line roughly 30 metres apart and slowly drive across the icefield.

When a sample is located on the surface, it is assigned an identification number and is given a position using Global Positioning System (GPS) technology. The field party will also take initial notes about its possible classification and any distinguishing features such as the fragment's shape and colour. The fragment is then bagged in a sterile Teflon bag and kept frozen until it reaches the Antarctic Meteorite Curation Facility at NASA's Johnson Space Centre (JSC) in Houston, Texas, where it is then analysed or sent on to another research facility.

Although he believes there is no efficient substitute for the human brain and eye, Borg says the use of GPS technology on these meteorite expeditions can be beneficial to researchers for a variety of reasons.

"For strictly meteorite research purposes, GPS locations in tens of metres are important in determining which fragments should be paired together, for instance, did they come from the same body that fell from space," he said.

"Often, several fragments are found even though they came from the same body, and sometimes those fragments are found in different seasons. Hence low-level GPS positioning is really useful to determine the location on otherwise pretty featureless ice surfaces."

Another way GPS is important is in understanding how the blue ice stranding surfaces work, Borg said. Blue ice is a term used for significant areas of ice that look light blue in colour. The colour is a result of the scattering of light in the ice.

Blue ice areas are found where the atmospheric conditions such as high wind and low humidity, preclude snow accumulation and cause the ice sheet to ablate(erode away via sublimation and wind abrasion). During this process, glacial ice, which originated as snow but got compacted into ice over time, is exposed.

In particular, GPS can help researchers understand how much blue ice ablates each year, Borg said.

"We know that surfaces can ablate 10cm or more, so if you can quantify this you can estimate the rate of flow into the region and address glaciological and climatological questions," he said.

In order to do this, researchers would place stakes in the surface sufficiently deep to be able to get several measurements for ablation rate calculations. For meteorites, researchers could use this type of information to estimate when field parties should go back to search again by estimating when new meteorites will surface as the ice ablates. In turn, this information could be used to estimate the concentration of meteorites in volumes of ice, he said.

- Dr Ralph Harvey of Case Western University is currently expedition leader for the ANSMET Program. More information on the expeditions can be found at:

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