Antarctica's icy plains are a magnet for meteorite hunters like Maria Valdes, a research scientist at the Field Museum of Natural History and the University of Chicago. About 1,000 space rocks are found in the region every year. Their dark hue is easily recognized in the white expanse.
"Antarctica, an icy desert, provides an ideal backdrop for the recovery of meteorites - go to the right place, and any rock you find must have fallen from the sky," said Valdes, who visited the region late last year as part of a expedition team. 2022 and early 2023 for her work in the museum's Robert A. Pritzker Center for Meteoritics and Polar Studies. The international team found five meteorites.
"We came across a huge brown rock sitting alone in the middle of an ice field. It was slightly smaller than a bowling ball and quite heavy: 7.6 kg (about 17 pounds)," she said via email. "I've seen and interacted with so many meteorites in my career, but finding one myself is such a different feeling."
Formed from alien bodies such as the moon, Mars or large asteroids, each meteorite tells a unique story about the solar system and how it was formed. But the climate crisis is threatening this wealth of scientific information, a new study shows. Meteorites disappear into the ice, putting them out of reach of scientists.
"As the climate continues to warm, Antarctic rocks are sinking into the ice faster and faster. This will eventually make many meteorites inaccessible to scientists," says Valdes, who was not involved in the latest research. "We are losing precious time capsules that hold clues to the history of our solar system."
As the Earth warms, about 5,000 meteorites could disappear from the surface of melting ice caps every year, according to the study published Monday in the journal Nature Climate Change. To date, more than 48,000 meteorites have been discovered in Antarctica, accounting for approximately 60% of the specimens found worldwide.
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How to find a meteorite
Meteorites, chunks of rock that fall randomly from space through Earth's atmosphere, do not fall in an evenly distributed pattern across the frozen continent. Concentrations arise in certain locations because of geography and weather patterns, Valdes explains.
Meteorites are especially abundant in blue ice fields. In these areas, a combination of ice flow processes and local weather conditions remove layers of snow and ice from the surface, exposing meteorites that were once embedded in the ice. The windblown ice tends to look blue compared to the surrounding surface snow.
"Over significant periods of time (tens or hundreds of thousands of years) phenomenal concentrations of meteorites can develop, in some locations as high as 1 per square meter," she said.
Researchers have identified areas of meteorite-rich blue ice largely by luck. To systematize the search, however, Veronica Tollenaar, a doctoral researcher at the Université Libre de Bruxelles in Belgium, and her colleagues used a machine-learning algorithm to create a "treasure map" of likely meteorite-rich zones, based on factors such as the surface temperature. , surface slope, surface cover and ice flow motion.
That study, published in January 2022 in the journal Science Advances, identified 600 zones and suggested that 300,000 meteorites are still present on the ice sheet's surface. Valdes said she and her colleagues in 2023 used the information to help inform their decision on where exactly to look during their expedition.
"Our experience... shows that Tollenaar's approach has only worked initially. Local parameters such as topography and wind directions that can redistribute meteorites from blue ice fields to local meteorite falls must also be taken into account," Valdes said.
In the new study, co-lead author Tollenaar and her team projected the loss of meteorites under different climate change scenarios by combining climate modeling with their work from the 2022 paper.
The meteorites can sink into the ice even at temperatures below zero degrees Celsius. The sun heats the dark rock, which due to its color absorbs solar radiation more easily, causing the surrounding ice to melt. "With that heat, the ice can melt locally and slowly disappear from the surface," says Tollenaar.
Harry Zekollari, who was co-lead author of the new study with Tollenaar, said cold surface temperature was one of four factors linked to a potential meteorite cluster.
"It's very important that it is cold and when your surface temperature starts to change, even if it goes from minus 12 degrees Celsius to minus 9 degrees Celsius, it crosses a magical threshold where you start losing meteorites," said Zekollari, associate professor glaciology at the Vrije Universiteit Brussel.
Under current policies, which the study says could result in warming of 2.6 to 2.7 degrees Celsius above pre-industrial levels, the researchers estimate that 28% to 30% of Antarctic meteorites could become inaccessible . In a high emissions scenario the estimate increased to 76%. Only at altitudes above 2,500 meters (8,202 feet) will meteorite losses be less than 50%, the study said.
Matthias van Ginneken, a research associate at the Center for Astrophysics and Planetary Science at the University of Kent in Britain, said the work "made a lot of sense when you consider how global warming appears to be affecting Antarctica."
However, Van Ginneken, who was not involved in the research, said he wished the authors had talked more about the uncertainties in their model and conducted laboratory experiments to simulate how global warming affects meteorites, which could affect the algorithm's results would support.
"It's certainly concerning, but there will still be thousands of meteorites found every year," he said by email.
"The biggest concern is the logistical aspect of searching for meteorites in Antarctica, which is already difficult today due to Antarctica's remoteness. Should the results of this study prove to be true, it will force scientists to explore new areas, possibly even further away from scientific bases than those typically explored. It would make this treasure trove even more inaccessible and thus require more funding and logistical support."
What we learned from Antarctic meteorites
Meteorites discovered in the southernmost reaches of the planet have taught us a lot, said Kevin Righter, a planetary scientist at NASA Johnson Space Center in Houston, in a commentary published alongside the study. He was not involved in the new investigation.
Scientists recognized meteorites collected in the region in 1979 and 1981 as coming from the moon, Righter noted. Before these finds, the only samples from the moon came from the Apollo and Luna landing sites. The meteorite samples have resulted in a more random and comprehensive sampling of the entire lunar surface. Other meteorites are connected to Mars.
"The entire recent history of research indicates that as collection continues, new types of meteorites are likely to be found - including perhaps pieces of Mercury or Venus thrown from their surfaces after impacts."
Righter, along with the study authors, called for increasing and prioritizing collection efforts. "If meteorites are not collected quickly enough, they will be a lost resource for current and future planetary science," he added.
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