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Sunlight shines on the snow-capped peaks of the Gerlache Strait in Antarctica.
Andrew Peacock / iStock.com
By Tess Joosse
Researchers have discovered a common Martian mineral deep in an Antarctic ice core. The discovery suggests that the mineral – a brittle, yellow-brown substance known as jarosite – was forged the same way on Earth and Mars: from dust trapped in ancient deposits of ice. It also reveals the importance of these glaciers on the Red Planet: not only did they carve out valleys, the researchers say, but they also helped create the very substance of Mars.
Jarosite was first spotted on Mars in 2004, when NASA’s Opportunity rover rolled it over fine-grained layers. The discovery made headlines because jarosite needs water to form, as well as iron, sulfate, potassium, and acidic conditions.
These requirements are not easily met on Mars, and scientists have begun to theorize how the mineral could have become so abundant. Some thought that she might have been left behind by the evaporation of small amounts of salty and acidic water. But the alkaline basalt rocks in the crust of Mars would have neutralized the acidic moisture, says Giovanni Baccolo, a geologist at the University of Milan-Bicocca and lead author of the new study.
Another idea was that jarosite was born in massive ice deposits that could have covered the planet billions of years ago. As the ice caps developed, dust would have accumulated in the ice and could have been turned into jarosite in pockets of slush between the ice crystals. But the process had never been observed anywhere in the solar system.
On Earth, jarosite can be found in mining waste piles that have been exposed to air and rain, but this is not common. No one expected to find him in Antarctica and Baccolo was not looking for him. Instead, he was looking for minerals that could indicate Ice Age cycles in the layers of an ice core 1,620 meters long., which record thousands of years of Earth history. But in the deepest ice of the core, he stumbled upon strange particles of dust that he believed to be jarosite.
To confirm the identity of the mineral, Baccolo and his collaborators measured how it absorbed x-rays. They also examined the grains under powerful electron microscopes, confirming that it was jarosite. The particles were also visibly cracked and devoid of sharp edges, a sign that they had formed and eroded as a result of chemical assaults in pockets in the ice, researchers report this month in Nature communications.
The work suggests that jarosite forms similarly on Mars, says Megan Elwood Madden, a geochemist at the University of Oklahoma who was not involved in the research. But she wonders if the process can explain the enormous abundance of jarosite on Mars. “On Mars, it’s not just a thin layer,” she says. “These are deposits several meters thick.”
Baccolo admits that the ice core contained only small amounts of jarosite, particles smaller than an eyelash or a grain of sand. But he explains that there is a lot more dust on Mars than in Antarctica, which receives only small amounts of airborne ash and dirt from northern continents. “Mars is such a dusty place – everything is covered in dust,” Baccolo says. More ash would promote the formation of more jarosite under the right conditions, he says.
Baccolo wants to use Antarctic carrots to determine if ancient Martian ice deposits were cauldrons for the formation of other minerals. He says the jarosite shows how glaciers were not just earth-carving machines, but could have contributed to the chemical makeup of Mars. “This is only the first step in connecting the deep Antarctic ice with the Martian environment.”
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