The brittle, tan mineral is rare on Earth, but surprisingly abundant on Mars. Geologists have now discovered it under Antarctic ice, suggesting that the mineral is formed when dust becomes trapped under ice deposits. In other words, glaciers didn’t just exist on Mars, but they contributed to the geological makeup of the planet.
Jarosite has been detected by three Mars rovers (Spirit, Opportunity and Curiosity). It is a hydrous sulphate hydrous comes from the Greek word meaning water because jarosite forms in the presence of water. Water is not only necessary for its formation, it is also necessary for its preservation. So when Martian robbers discovered it on the Red Planet, it was a strong nod to a wet past. Now researchers have found it in Antarctica too; deep in Antarctica.
The discovery came from the Talos Dome Ice Core (TALDICE) project in East Antarctica, a European research project. The project looks at signs pointing to our planet’s past climate, but it turns out that a team of researchers led by Giovanni Baccolo from the University of Milano-Bicocca in Italy has also learned something about the climate of Mars.
The mineral requires very specific conditions to form: it needs water (but not too much) and acidity – not exactly conditions you can find on the Red Planet right now. So when the mineral was first found on Mars in 2004, it initially confused researchers. After that, it kept popping up, showing that the initial discovery was no accident and tasked geologists with figuring out how the mineral formed on Mars.
Jarosite is not very common here on Earth. We know that it can form as a result of the low-temperature acidic weather of ferrous minerals and as a product of zinc refining (which, of course, you wouldn’t expect on Mars). So the cold, sour weathering theory seemed more likely, but the smoking gun was missing so far.
The mechanisms behind jarosite formation had been theorized, but never seen before, neither on Earth nor beyond. The jarosite samples were found in a Talos ice core more than 1,000 meters (3,281 feet) below the ice. The crystal weathering suggests that the minerals that formed there (and in fact the ice was undisturbed for 250,000 years), so this is likely where the minerals formed – the smoking gun.
“Based on our understanding of the environmental conditions of deep ice, we interpret jarosite as the product of glacial weathering,” the researchers write in their paper.
“Its formation requires acidic conditions, limited liquid water activity and the presence of ferrous materials. The deep part (> 1000 m) of TALDICE can meet such requirements. “
Likewise, since jarosite is so common now on Mars, it likely means the planet must have had massive ice masses that formed its surface – and recent research agrees. Separate studies suggest that Mars had multiple Ice Age periods, much like Earth, and that Mars has experienced dramatic climatic fluctuations throughout its history. As the ice sheets grew over time, dust is said to have accumulated and form jarosite in muddy pockets.
But there is one more question.
The Antarctic survey revealed a thin film of jarosite and only in one place (so far), but Mars has thick, meter-sized deposits, so the conditions for jarosite formation must have been much better on Mars. Perhaps this could be explained by dust: Mars is much more dusty than Earth, and there would have been more ‘seeds’ to form jarosite.
The study is published in the journal Nature Communications.