In a study recently published in the Journal of Geophysical Research: Planets, researchers from the University of Arizona used drones equipped with ground-penetrating radar to learn more about two debris-covered glaciers in the US.
These so-called ‘buried glaciers’ bear striking resemblance to buried ice deposits observed on Mars and could therefore guide the search for water on the Red Planet.
The classic image of a glacier is a large, dusty-white river of ice flowing down the side of a mountain, exposed to the elements. Not all glaciers look like this; debris-covered glaciers are – as their name suggests – covered by thick layers of rock and sediment.
These kinds of glaciers only make up 5% of glaciers globally, but they’re found in mountainous regions across the world, including in warmer areas such as Colorado and California, where debris insulates the ice underneath and stops it from melting.
On Mars, similar-looking, debris-covered glaciers are found in mid-latitude regions. According to Roberto Aguilar, the lead author of the latest study, these glaciers are found in craters, large valleys and mountainous regions where ice has accumulated and later been buried by debris.
Like it does on Earth, debris shields the underlying ice, preventing it from melting and evaporating into the atmosphere.
“Some of these deposits are large enough that radars on orbiting spacecraft can detect and estimate the amount of ice, but current technology cannot determine fine details, such as how thick the overlying debris layer is, or if there are internal, rocky layers hidden from view,” Aguilar said.
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In order to solve this problem, Aguilar and his colleagues experimented with a drone-based radar system specifically designed to detect the boundary between debris and underlying ice, as well as shallow layers within the bodies of buried glaciers themselves.
This involved flying a drone equipped with ground-penetrating radar over two Earth-based analogs for Martian glaciers: Sourdough Rock Glacier in Alaska and Galena Creek Rock Glacier in Wyoming.
“We already knew ground-penetrating radar works, but this was the first time we mounted it to drones and tested how we could put it into practice,” said Aguilar. “For instance, we learned at what altitude and speed the drone should fly, as well as the importance of flying in the direction of the glacier’s flow, and how to make sure the radar was properly aligned to detect the ice.”
As drones are able to fly much closer to the surface of a glacier, they’re able to capture images at much higher resolutions. This allowed the researchers to not only estimate the debris thickness covering the buried glaciers in Alaska and Wyoming, but also assess the purity of the ice and spot any rocky layers hidden inside.
“The internal layers we’re seeing are important because they’re a record of past climate cycles,” Aguilar said. “Each layer represents a different period of ice accumulation and environmental conditions over centuries or millennia, and it is likely we would see similar layers on Mars.”
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To validate their methods, the researchers compared measurements obtained from the ground-penetrating radar with those from excavating and drilling into the buried glaciers. These debris thickness measurements matched, suggesting drone-radar surveys could be performed on Mars with similar levels of success.
The researchers also ran simulations to discriminate real subsurface features from reflections caused by nearby surface features, such as trees or boulders, and were able to confirm that the signals were indeed coming from the buried glaciers.
“We are filling the gap between today’s orbital observations and a more distant future, where astronauts land on Mars and make observations on the ground,” said Aguilar. “This gives us a way to investigate the glaciers now, from the air.”
Using these pioneering methods, Aguilar and others hope that future missions to Mars will be able to identify the best areas to drill into buried ice deposits and extract water that has been locked beneath the surface for more than four billion years. The study of this extracted water will reveal more about Mars’ past climate and potential habitability to extraterrestrial life.
On Earth, scientists have discovered microbial ecosystems inside the bodies of buried glaciers. These microbes live in thin films of water between ice crystals and gradually break down rocks, which releases nutrients such as iron, phosphorus and silicon into meltwater. While the chances of discovering similar living microbes on Mars may be slim, buried ice deposits hold the best potential for finding evidence that such life may have once existed.
Top image: Obscured by rocky debris, the Sourdough Rock Glacier flows down from the Wrangell Mountains in Alaska. Credit: Eric Petersen
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