Antarctica is 'meteor hotbed'
UNM's Cohen braves tundra conducting meteoritic research
By Steve Carr
|UNM Earth and Planetary Sciences Research Assistant Professor Barbara Cohen, center right, photographs a meteorite buried in the frozen Antarctic tundra. Cohen was one of 10 researchers selected to participate in the Antarctic Search for Meteorites program, funded by the National Science Foundation and NASA. See full story on page 4. Photo by Cordon Osinski.
There are probably better places to spend 40 days than searching for meteorites in the frozen, wind blown tundra of Antarctica, but for Research Assistant Professor Barbara Cohen in the UNM Department of Earth and Planetary Sciences, it was the opportunity of a lifetime.
As part of the Antarctic Search for Meteorites (ANSMET) program, funded by the National Science Foundation (NSF) and NASA, Cohen was one of 10 researchers selected to participate in the latest expedition this winter (summer in Antarctica).
Antarctica is a hot bed of meteorites. More than 25,000 have been collected under the ANSMET program, which began in 1976 when the NSF provided support for a meteorite expedition led by researcher Bill Cassidy. Cohen’s group found more than 1,300 meteorites on their trip.
Meteorites have fallen randomly over the earth’s surface throughout time. The best place to find meteorites is in dry environments like the Antarctic. Water causes meteorites to weather. Snow accumulates, along with the meteorites, in the accretion zone. Then, due to its own weight, it becomes compacted and flows downward, turning snow into a glacier. At some point, the glacier flow is interrupted due to an obstruction, like a mountain, Cohen says.
Cold atmospheric air sinks over the South Pole. The cold air flows to a low place causing winds up to 80 knots. The dry, cold winds erode the ice away and leave concentrations of meteorites at the base of the mountain waiting to be picked up. Meteorite hunters search for areas of blue ice, which are seemingly endless expanses of nothing but clean ice from deep within the Antarctic ice sheets. It is blue for the same reason the sky is blue. Water scatters blue light preferentially, resulting in an astonishingly deep color. When hunters find areas like this, they are sure any rock found had to have fallen from the sky, Cohen says.
Another good place to find meteorites is in sandy deserts such as the Saharan in Africa, where sand is always shifting. Meteorites stay where the sand has blown away causing a concentration effect.
Once found, the meteorites, which are generally less than one centimeter on a side, are kept frozen and put on a boat to California, then trucked to NASA’s Johnson Space Center in Houston where they are opened up under nitrogen. The meteorites are then unpacked and stored in nitrogen because it displaces water and oxygen in the atmosphere.
Cohen’s research team hopes that among the 1,300 meteorites found, some might turn out to be lunar or Martian meteorites.
The meteorites then go to the Smithsonian Institute in Washington, D.C. to a team of scientists who classify the meteorites and send them back to the Johnson Space Center for curation and dissemination to the research community.
Cohen’s research team hopes that among the 1,300 meteorites found, some might turn out to be lunar or Martian meteorites, although they will not know the outcome until late summer.
Finding the meteorites is one thing, while surviving the conditions in the Antarctic, where there is daylight 24 hours a day during the summer, is quite another.
Cohen’s team was at a self-contained remote field camp, living in two-person tents. They searched for meteorites at La Paz Ice Field, named for Lincoln La Paz who actually founded the UNM meteorite collection and Institute of Meteoritics. Cohen said it was very bright and so team members had to wear goggles with UV protection. Wind limited their ability to stay out long to search for meteorites.
Usually the temperature was -15 Celsius (5 degrees Fahrenheit) with winds of 20 knots for a wind chill of
-27 Celsius (-16 Fahrenheit).
On good days, they were able to stay out for about eight hours looking for meteorites.
About one in five days the weather was so bad they couldn’t work, says Cohen, who read “War and Peace” in its entirety while in Antarctica.
In addition to her recent meteorite expedition, Cohen is researching the impact and geochemical history of the moon and asteroids.
She is also helping out on the renovation of the UNM Meteorite Museum.