Wednesday, June 29

A mineral found in Antarctica may solve a Mars mystery

Jarosite fragment collected in Almería

Jarosite fragment collected in Almería

A A mineral common on Mars but rare on Earth has been found deep within an Antarctic ice core, and can solve a mystery of the Red Planet.

The finding suggests that the mineral, a brittle, yellowish-brown substance Known as jarosite, it was forged in the same way on both Earth and Mars: from dust trapped in ancient ice deposits. It also reveals the importance of these glaciers on the Red Planet: not only did they excavate valleys, the researchers say, but they also helped create the very matter that Mars is made of.

Jarosite was first seen on Mars in 2004, when NASA’s Opportunity rover passed over fine-grained layers. The discovery made news because jarosite needs water to form, along with iron, sulfate, potassium, and acidic conditions.

These requirements are not easily satisfied on Mars, and scientists began to theorize how the mineral could have become so abundant. Some thought it may have been left by the evaporation of small amounts of acidic and salty 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 inside massive ice deposits that could have covered the planet billions of years ago. As the ice sheets grew over time, the dust would have accumulated inside the ice and it may have transformed into jarosite within muddy pockets between the ice crystals. But the process had never been observed anywhere in the Solar System.

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On Earth, jarosite can be found in heaps of mining waste that have been exposed to air and rain, but it is not common. No one expected to find it in Antarctica and Baccolo was not looking for it. Instead, he was looking for minerals that could indicate ice age cycles within the layers of a 1,620-meter-long ice core, which records thousands of years of Earth’s history. But in the ice deeper in the core, he encountered strange dust particles that he thought might be jarosite.

To confirm the identity of the mineral, Baccolo and his collaborators measured how it absorbed X-rays. They also examined grains under powerful electron microscopes, confirming that it was jarosite. The particles were also noticeably cracked and lacked sharp edges, a sign that they had been formed and eroded by chemical attack on pockets within the ice, the researchers reported this month in Nature Communications.

The work suggests that jarosite forms the same way on Mars, says Megan Elwood Madden, a geochemist at the University of Oklahoma who was not involved in the research. But he wonders if the process can explain the enormous abundance of jarosite on Mars. “On Mars, this is not just a thin film“he says.” These are meter-thick deposits. ”

Baccolo admits that the ice core contained only tiny amounts of jarosite, particles smaller than an eyelash or grain of sand. But he explains that there is much more dust on Mars than in Antarctica, which only receives small amounts of airborne ash and dirt from the northern continents. “Mars is a dusty place, everything is covered in dust,” Baccolo told Science Magazine. More ash would encourage more jarosite to form under the right conditions, he says.

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Baccolo wants to use Antarctic cores to investigate whether ancient Martian ice deposits were cauldrons for the formation of other minerals. He says the jarosite shows how the glaciers weren’t just machines for carving the earth, they could have contributed to the chemical makeup of Mars. “This is just the first step in linking deep Antarctic ice with the Martian environment. ”

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