Sunlight shines on the snow-capped peaks of Gerlache Street in Antarctica.
Andrew Peacock / iStock.com
By Tess Joosse
Researchers have discovered a common Martian mineral deep inside an Antarctic ice core. The find suggests that the mineral – a brittle, yellow-brown substance known as jarosite – was forged in the same way on Earth and on Mars: from dust trapped in ancient ice deposits. It also reveals how important these glaciers were on the Red Planet: according to the researchers, they not only carved valleys, but also helped create the things Mars was made of.
Jarosite was first spotted on Mars in 2004 when the NASA Opportunity Rover rolled over fine layers of it. The discovery made headlines because jarosite needs water to form, along with iron, sulfate, potassium and acid conditions.
Mars does not easily meet these requirements, and scientists have begun to theorize how the mineral could become so abundant. Some thought it might have been left behind by the evaporation of small amounts of salty, acidic water. But the basic basalt rocks in Mars’ crust would have neutralized the acid moisture, says Giovanni Baccolo, a geologist at the University of Milan-Bicocca and lead author of the new study.
Another idea was that the jarosite was born within massive ice deposits that may have covered the planet billions of years ago. As ice sheets grew over time, dust would accumulate in the ice – and could turn into jarosite into soft bags between ice crystals. But the process has never been observed in the Solar System.
On earth, jarosite can be found in heaps of mining debris exposed to air and rain, but this is not common. No one expected to find it in Antarctica, and Baccolo did not look for it. Instead, he looked for minerals that could indicate ice age cycles in the layers of an ice core of 1620 meters, which records thousands of years of the earth’s history. But in the deepest ice of the core, he came across strange dust particles that he thought might be jarosite.
To confirm the identity of the mineral, Baccolo and his collaborators measured how it absorbs x-rays. They also examined grains under powerful electron microscopes and confirmed that it was jarosite. The particles were also noticeably cracked and without sharp edges, a sign that they had formed and eroded from chemical attacks in bags in the ice, the researchers reported this month in Nature communication.
The work suggests that jarosite forms in the same way 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 could explain the large amount of jarosite on Mars. “On Mars, it’s not just a thin film,” she says. “These are meter-thick deposits.”
Baccolo admits that the ice core contains only small amounts of jarosite, particles smaller than an eyelash or a grain of sand. But he explains that there is much more dust on Mars than in Antarctica, which receives only small amounts of ash and dirt from the northern continents. “Mars is such a dusty place – everything is covered in dust,” says Baccolo. More than will benefit more jarosite formation under the right conditions, he says.
Baccolo wants to use Antarctic nuclei to investigate whether ancient ice deposits from Mars were a kettle for the formation of other minerals. He says jarosit shows how glaciers were not just carving machines, but possibly contributed to Mars’ chemical composition. “This is just the first step in connecting deep Antarctic ice with the martial environment.”