The Antarctic ice is home to stuff “not of this Earth.”
Each year, scientists travel to remote sections of the frozen continent to look for these pieces of outer space. They’re hunting for meteorites; the charred remains of asteroids and other space debris that fell to Earth. This year, after five weeks out in the field, the eight-person Antarctic Search for Meteorites (ANSMET) team returned with 569 likely meteorites.
“That’s a good haul,” said James Karner, a scientist at Case Western Reserve University and co-principal investigator on the project. “In that bunch I think there’s the potential for about dozen or so to be really special meteorites, kind of rare ones.”
In coming months, these samples will be processed at NASA’s Johnson Space Flight Center, and made available to researchers around the world to study. The project is funded by NASA and the field work is logistically supported by the National Science Foundation (NSF), which manages the U.S. Antarctic Program.
The search for meteorites is but one of the ways in which Antarctic serves as a globally unique natural research laboratory, accessible to U.S. researchers only through the support provided by the Antarctic Program.
“What we’re trying to do is understand the formation of the solar system, and how the planets themselves formed,” said Constantine Tsang, a planetary scientist at the Southwest Research Institute. “[Meteorites] give us a direct measurement of the distant past that you could never get any other way… There’s actual material that’s been preserved in space for that amount of time.”
Antarctica is the ideal place on Earth for meteorite hunting. Roughly two-thirds of all meteorites available to researchers were found on the icy continent.
“You need two good things to make meteorite collection efficient and economical. One you need to lay out a big white sheet and see what falls from the sky. Of course Antarctica fits that really, really well,” said Ralph Harvey of Case Western Reserve University and the primary principal investigator for the project. “The other is you want to work in a place where the input of earthly debris, terrestrial debris, is really low and that relatively speaking, accentuates the amount of extraterrestrial stuff.”
There are numerous big, barren ice fields across the continent that fit the bill perfectly, and over the years, the teams have been systematically exploring these areas. This year, the team set up camp at the foot of the mountains in the Miller Range, a region about halfway between McMurdo Station and the South Pole.
“It’s gorgeous out there,” Karner said. “It’s just a lot of rocks and ice and when you’re out there there’s no sound or human contamination at all. It’s just us and the ice and the rocks out there.”
This was the team’s eighth visit to the area. It’s a region where geologic processes produce a hard surface of blue ice, making for ideal meteorite recovery. Ice takes on a blueish hue at the bottom of glaciers, where tremendous pressures squeeze the frozen water molecules tightly together. To see blue ice at the surface, it means that over countless years, natural processes have stripped away the younger, uppermost layers, leaving behind only the older, azure-colored layers from the base of the glacier.
“Along with this old ice being forced up to the surface, it brings the things that are traveling along in the ice up with it, which means rocks and meteorites,” Karner said.
In these blue ice regions, the ice surrounding ancient embedded meteorites evaporated away, leaving the meteorites on the surface, ready for recovery. The cold, dry climate of Antarctica preserves them while they’re lying out on the surface. Even while buried inside the ice, the meteorites are protected. The ice encasing stays frozen so it doesn’t react with them and affect the sample.
“The meteorites in Antarctica are some of the least terrestrially altered meteorite samples that you can get your hands on,” said Ellen Crapster-Pregont, a graduate student at Columbia University. “Antarctica is a perfect repository for these specimens, not only because it’s a desert, which limits the effects of terrestrial weathering, but also because of the ice dynamics.”
Traveling to the deep field of Antarctica may seem like a long way to collect meteorites, but compared to where the space rocks originated from, it’s hardly any distance at all. Over the years, teams have found samples from Mars, the moon, the asteroid Vesta and numerous other smaller bodies distributed throughout the solar system.
“This is really a cost-effective way to sample throughout the solar system,” said Nina Lanza, a researcher at Los Alamos National Lab. “We’re able to sample all of these planetary bodies without leaving home. That’s a real bargain in terms of planetary science.”
There’s never been a space mission that brought back samples from the planet Mars and of the handful of meteorites that scientists identified as originating from the red planet, the vast majority were discovered as Antarctic meteorites.
“They’re the equivalent of a visit to places that we just have no hope of visiting in the short term. They’re a way of exploring our solar system by waiting at home to see what’s out there, having it delivered,” Harvey said. “That’s what meteorites do and they do it for minuscule fraction of what space missions cost.”
There are also political reasons that make Antarctic collection viable.
“It can be hard to get meteorites from some places in the world,” said Morgan Martinez, who just defended her doctorate at the University of California in San Diego before joining the team. “But because the Antarctic treaty protects Antarctica for research and not profit purposes, we’re able to collect those meteorites and the community can have access to the meteorites without having to pay for the samples themselves to an individual or to a government or something like that.”
This upcoming season will be ANSMET’s 40th field season. Each year, the eight-member team is made up of different volunteers culled from the planetary science community. It’s one of the only science projects in the Antarctic Program that takes volunteers and there are new faces each season.
“It really injects a lot of energy to have some new people every year,” Harvey said. “The other benefit of it is when we can give meteorite researchers some exposure to the objects they work on and they can understand a lot more about how they got to be the way they are.”
Though they’re looking for extra-terrestrial samples, the search itself is pretty low-tech. There are no special tools or high-tech devices that can detect space rocks from afar. The team members rely on visual cues to distinguish meteorites from any ordinary, terrestrial rocks that are lying around.
“After a while your eye gets tuned into these very subtle distinctions,” said Cynthia Evans, the manager of NASA’s Astromaterials Acquisition and Curation Office at Johnson Space Center. She’s in charge of the office that receives the samples once they’re brought to the United States, and joined the search team to get a better understanding of where the samples come from.
On wide-open sections of ice, the search is easier. These ice plains can be so big, that the only way for a rock to wind up in the middle of it is for it to have fallen from space. In areas where there are other rocks around, they look for the dark, smooth fusion crust that’s shows that a rock fell to Earth.
“As a rock from space falls through the Earth’s atmosphere, and it starts to burn up, they form this black fusion crust. The silica basically starts melting and reforms a coat that’s extremely black and shiny,” said Tsang. “You have this very black patina that forms on these meteorites against the white or blue backdrop of the ice, so it makes searching much easier for us.”
This black outer layer stands out starkly against the white and blue ice it rests on. Even when there are other rocks nearby, it lets the meteorites stand out.
“The fusion crust is definitely the best, telltale sign,” said Crapster-Pregont. “Otherwise, you get really familiar with the terrestrial rocks, and if a rock doesn’t look like any of the terrestrial rocks in the area that you have ever seen, then it’s most likely an extraterrestrial rock or a meteorite of some kind.”
Though there are countless meteorites throughout the continent, they’re sparsely distributed. So in order to collect an appreciable amount of samples, the team members have to cover a lot of ground.
The majority of the time the team is hunting for samples from the back of their snow machines. The team members ride in a grid pattern, with snowmobiles usually spaced about 30 feet apart. Everyone keeps their eyes on the ground, looking for any dark lumps sticking out against the blue ice. It’s a carefully planned, systematic search so that future teams can come in and fill in gaps during subsequent seasons.
“Mostly we’re cruising around on snowmobiles,” Martinez said. “Sometimes we go to areas where there are higher concentrations of terrestrial rocks, like the moraines, and in those places we’ll get off the snowmobiles and search on foot.”
For eight hours a day, they drove along at about five miles an hour, scanning the ice. When they come across anything unusual, they’ll go in for a closer look. No sample is too small to be investigated.
“Every time that we see a rock, we stop,” Lanza said. “When we think we found a meteorite you make the international sign for ‘come here’ which is waving your arms in an X.”
If the rock looks promising, they’ll collect it and send it back to the United States for full identification.
Without ever touching the sample directly, members of the team photograph it, write down a few notes about its surroundings and estimate its dimensions before using tongs to place it in a sterilized plastic bag with an identification tag. After it’s bagged and tagged, each sample is carefully placed in the collection box, and the team resumes their search.
At the end of the season, all of the samples are flown in a refrigerated shipping container back to McMurdo Station, where they’re kept in sub-zero temperatures, until the container is loaded onto a cargo vessel headed to Port Hueneme in California. While still frozen, they’re driven halfway across the country to the Johnson Space Center in Houston Texas.
Once they reach the center’s meteorite lab, scientists start to analyze them more carefully to determine what kinds they are and where in the solar system they may have originated. They’ll get catalogued, and carefully thawed.
“They will be very slowly dried out under nitrogen because we don’t want them to rust,” Evans said. The meteorites will stay in boxes filled with pure nitrogen as they’re carefully measured and sliced into thin sections that are most useful to researchers. “Once that’s complete the samples will get announced; once a sample is announced it’s available to the community to study.”
Any researcher in the world studying planetary science can look at the catalog and apply to receive samples. Like taking a book out of the library, these scientists will be the ones conducting research and making new discoveries with the recovered meteorites.
“ANSMET itself is more service than science,” Harvey said.
The idea is to build up as large a library as possible of samples from the far reaches of the solar system. Already the program has collected more than 21,000 meteorites over the 40 seasons it’s been operating. But Harvey says that there are still a lot of unexplored sites to visit and new samples to collect.
“It may seem like we have a huge collection of meteorites, but in fact these meteorites represent a really really rare event where a little bit of stuff out in the solar system gets in the way of the Earth and its orbit,” Harvey said. He added that the collection is really only just beginning. “We’re at a place where there are still huge holes in our catalogue.”
Most of the meteorites in the collection are what are known as chondrites, stony space rocks that are leftovers from when the solar system was first coalescing out of clouds of dust and gas more than 4.5 billion years ago. They come from asteroids that were never part of a celestial body large enough for gravity to separate it into a core, mantle and crust. Chondrites are essentially the building blocks of planets and moons that never quite made it into one, and they give scientists an unprecedented window into the primordial history of our corner of the cosmos.
When the team comes across more unusual finds, like pieces of the asteroid Vesta, Earth’s moon and Mars, they get a chance to learn more about the planetoids they originated from. These rocks not only tell scientists about the history of distant space bodies, but can help them understand more about Earth’s own past.
“We see a history of Mars written in those rocks that suggest a planet where water was going away and the climate was changing, and you naturally kind of wonder why… Why did the water stay on our planet, or have we lost water and didn’t even know it,” Harvey said. “We can answer these questions for our own planet, or try to, but it’s really really good to have a second planet to use as a counterexample or as a control.”
There are surely countless more meteorites from all corners of the solar system waiting to be discovered across Antarctica. NASA just funded the program for another five years and though Harvey said that their work around the Miller Range is nearly done, there are numerous more areas they’ve identified that look promising.
“The problem now is more along the lines of ‘Can we get someone there? Can we get some boots on the ice and look around?’” Harvey said. “We still have dozens of places we’d like to go to, and dozens of seasons more work out in front of us.”
NSF-funded research in this article: Ralph Harvey, Case Western Reserve University, Award No. 0839168
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