In this month’s “Meet a SI-entist,” Corrigan discusses her work gathering meteorites in Antarctica, those specimens’ scientific value and what happens after they reach the museum’s National Meteorite Collection.
The journey from space to Earth is not an easy one for most meteorites. But post-arrival plans are more comfortable for the lucky ones collected by Cari Corrigan, planetary geologist at the Smithsonian National Museum of Natural History.
You’re a research geologist who studies meteorites from Antarctica. What led you down this path?
As an undergraduate student, I took an astronomy course that led me to take a geology class. My professor in that class told me about this field called planetary geology. So, I declared geology as a major and it turns out my advisor was the only person in this university who dabbled in planetary geology. He helped me do independent study, which led me to an internship working at NASA’s Lyndon B. Johnson Space Center on meteorite research. The scientist I worked with there had been to Antarctica. It was the first time I had heard of anyone going to Antarctica to collect meteorites.
The meteorite shown is slightly larger than Corrigan’s typical finds. Most Antarctic meteorites are golf ball sized.
During that summer, I also met Tim McCoy, the NMNH’s current curator-in-charge of meteorites, who was a post-doctoral researcher back then. All the people that I met that summer ended up being the people I’ve worked with ever since. It was a crazy, life-changing experience and one of those “right place at the right time” kind of things. Never did I think to myself when I was first getting my degree that I would get a job studying meteorites and get to go to Antarctica.
Why do you go to Antarctica for meteorites? Don’t they fall elsewhere as well?
Meteorites fall everywhere on Earth. Of course, 70% of them fall in the water somewhere, because 70% of our planet is ocean. We lose a heartbreaking number of specimens that way. But meteorites are easier to find in Antarctica, because of the environmental conditions. Sometimes, you’re on the ice where there are not any other rocks around besides meteorites. That’s because Antarctica’s structure is like a big dome with the South Pole roughly in the middle. Gravity makes ice flow out to the edges of the continent and the Trans-Antarctic Mountain Range runs across the middle of the continent. In some places, you’re above those mountains and the ice is so thick that any rocks you see have to have come from above. There are no terrestrial rocks to be found.
Meteorites have been falling and being buried by snow and ice for thousands of years. The ice flows down towards the coasts and gets stuck against the Trans-Antarctic mountains. The dry winds and sublimation remove the ice, leaving meteorites stranded on the surface. We call these areas stranding surfaces and we don’t totally understand why the meteorites are concentrated there. It isn’t like one meteorite came in and broke up. It’s all different kinds of meteorites. Corrigan searches through a glacial stranding surface for meteorites, which have a distinguishable glassy crust that makes them look different than terrestrial rocks.
ANSMET This second type of meteorite collection location — these stranding surfaces — can also have terrestrial rocks. How do you spot the difference between those and meteorites?
What types of meteorites are there lying around? Most of them are ordinary chondrites. The reason they’re called chondrites is because they have small objects in them called chondrules. Each chondrule was a molten droplet out in the solar system over 4.5 billion years ago and those came together to form asteroids. Roughly 98% of all meteorites are chondrites of some sort. There are also some that have a little more carbon in them, which are called carbonaceous chondrites.
There’s something called a fusion crust that forms on meteorites as they pass through Earth’s atmosphere. They’re going so fast that friction melts the outside of the rock, which ends up with a layer of glassy crust. It’s pretty easy to spot that on meteorites. Also, your eye gets used to looking for the differences. Spend a day looking in a giant field of rocks on ice and you’d also be able to spot the meteorites really quickly. The stranding surfaces are found on the glaciers. That glaciers’ movement has scraped the rocks off the sides of these mountains, so there are certainly places where you have terrestrial rocks. But the difference can be obvious.
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