22 January, 2003
Hello from a very blustery McMurdo. It’s Linda Welzenbach reporting. Andy and the rest of the male contingent managed to sneak out on a late Sunday flight to Christchurch on a C-141. A very lucky escape as within just a few hours we were enveloped in a blizzard. Condition 1 was listed on the weather channel for all areas outside of McMurdo station and Scott Base, which means absolutely no travel except in an emergency, and even then requires an escort by Search and Rescue personnel. McMurdo itself was Condition 2, which allows foot travel. Some events are not weather dependent, so at 7:45 last night, we helped Dean with Bag Drag, the required weighing in for a Tuesday flight north, which we knew would be cancelled. Getting outside was actually refreshing, so we made the best running around in winds gusting to 50 knots, and glasses completely covered in wet snow. We did manage to have a little bit of photographic fun as you can see below…
Now that we have finished collecting, we thought it might be a good idea to explain what happens to the meteorites once they leave Antarctica. They are currently held in a freezer until the boat arrives that will carry them frozen back to the U.S. The estimated date of arrival is the 8th of March, at which point they will be flown to NASA’s Johnson Space Center in Houston. As many of you will know, that is also where the Lunar Rocks were initially processed and where they still live. This made it pretty easy for the ANSMET founders to decide who would be the best custodian and handler of the meteorites collected.
It should be no surprise that the meteorites are unpacked in the same cabinets used to process the lunar rocks. These cabinets are filled with Nitrogen gas, which is used to dry out any ice or snow that adhered to the meteorites when they were collected. The gas also keeps out moisture, salts, metals and organic compounds for as long as the meteorites remain stored in that environment, preserving them for the future. After they’ve been thawed and dried, they are weighed, described, photographed and given a name.
So what’s in a meteorite name? All the worlds’ meteorites are named for the local geographic landmark or township from which they are found. While there are numerous Antarctic locations (almost 40!) naming the hundreds of meteorites found at each would be difficult. Yet it is actually a very simple system of letters and numbers that is used to keep track of all those pesky meteorites. A typical Antarctic meteorite will have a name that looks like this: BTN 00300, where the first three letters are the abbreviation of the location (in this case Bates Nuntak.) The first two numbers are the year it was collected (2000-but we only use the last two digits), and the last three digits refer to the specimen number among all the meteorites collected in that year.
After NASA has curated and cataloged the meteorite, they remove a few grams and send it to me at the Smithsonian for identification and description. When I receive the package from NASA, I conduct a macroscopic investigation of the chips, separating out the unique chondrites, achondrites and irons for in-depth analyses, while the rest of the ordinary chondrites are set aside to be classified using standard optical mineralogy methods.
First, let’s look at what we do with those we decide require in-depth analyses. These will go to our Polished Thin Section preparator, who will take the chip, impregnate it with epoxy, glue it to a * inch round glass slide, cut off most of the sample (the remainder is used to make future thin-sections) and grind the remainder down the a thickness of 30-40 microns (please folks, don’t try this at home, it’s a job for a professional!) At this thickness you can see through the rock. When placed under a microscope, you see a kaleidoscopic view of all of the individual minerals, how they are connected to each other, and using an Electron Microprobe, find out the chemical make-up of the individual mineral crystals. We can also describe what kind of textures and structures are present.
For the ordinary chondrites, we actually remove a small piece from the chip to make into a powder for classification using a petrographic microscope. The process is relatively simple, but takes 5-7 minutes for each sample (Imagine how long it would take to process more than 800 from this season….). We grind the tiny sample into a powder (tiny mineral crystals,) and immerse them in special optical oils on a glass slide. Our observation of optical effects that occur between the crystal and the oil tell us something about the iron content of the mineral, which then can be applied to a system of classifying ordinary chondrites.
Now that all the meteorites are classified, we send the data back to JSC, where it will be published in the Antarctic Meteorite Newsletter. Published twice per year, scientists all over the globe will read it to find out about all the new meteorite samples now available for research. NASA’s stewardship goes beyond it’s initial handling of the meteorites collected, they also handle scientists requests for samples, up to 75 per year for an average of 600 samples. In the 26 years the program has been operating. over 300 investigators from 24 nations have received over 10,000 samples.
In addition to NASA’s curatorial duties, the National Science Foundation sponsors a committee of meteorite scientists, called the Meteorite Working Group, who aid NASA by assisting with sample allocations for meteorites whose rarity and limited quantity need to be preserved for the future.
What NASA doesn’t have is unlimited space, and here is where the Smithsonian becomes involved again. After a certain period of reduced activity, certain meteorites are transferred to the Smithsonian. As committed to preservation as NASA, the Smithsonian modeled its storage exactly like the Lunar and Meteorite facility at the Johnson Space Center, located out at our Museum Support Center in Suitland, MD.
Besides supporting a continually active sample allocation program, we are parcticipate in extensive outreach programs, such as exhibition of Antarctic meteorites, not only at the National Museum of Natural History, but all over the world, including at the Antarctic Treaty Conference scheduled for June 2003 in Madrid, Spain.
The next time you see an Antarctic meteorite, you will have the soup to nuts understanding of what it took to get it from the ice, to the world. I’m so glad to be a part of the world of Antarctic meteorites, and I’m pleased to be able to share it with you.
For more information, you can go to the following websites: http://www-curator.jsc.nasa.gov/curator/antmet/antmet.htm http://www.cwru.edu/affil/ansmet/
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