Dusty selfie from the Curiosity rover. Photo: Europa Press.

Scientists at Washington University in St.Louis have experimentally proven that, under Mars-like conditions, manganese oxides can easily form without atmospheric oxygen. When NASA Mars explorers found manganese oxides in rocks from Mars’ Gale and Endeavor craters in 2014, the discovery prompted some scientists to suggest that the red planet may have once had more oxygen in its atmosphere billions of millions ago. of years. But the new study, published in Nature Geoscience, radically changes this point of view.

The minerals likely required abundant water and strongly oxidizing conditions to form, the scientists interpreted. Drawing on lessons learned from Earth’s geologic record, they concluded that the presence of manganese oxides indicated that Mars had experienced periodic increases in atmospheric oxygen in the past, before dipping to current low levels.

Carbon dioxide But now, using kinetic models, the scientists have also shown that oxidation of manganese is not possible in the carbon dioxide-rich atmosphere expected on ancient Mars. “The relationship between manganese oxides and oxygen suffers from a number of fundamental geochemical problems,” Jeffrey Catalano, Professor of Earth and Planetary Sciences in Arts and Sciences and corresponding author of the study, said in a statement. Mars is a planet rich in the halogen elements chlorine and bromine compared to Earth. “Halogens occur on Mars in different forms than on Earth and in much larger quantities, so we assumed that they would be important for the fate of manganese,” explains Catalano.

Catalano and Kaushik Mitra, currently a Stony Brook University Postdoctoral Research Associate, who did this work as part of his graduate research at the University of Washington, conducted laboratory experiments using chlorate and bromate — the dominant forms of these elements in Mars– to oxidize manganese in water samples that were made to reproduce the fluids on the surface of Mars in the ancient past.

Extremophile organisms that can survive in a halogen-rich environment, such as the salt-loving single-celled organisms and bacteria that thrive in the Great Salt Lake and Dead Sea on Earth, could also do well on Mars. “We need more experiments conducted under diverse geochemical conditions that are more relevant to specific planets like Mars, Venus, and ‘ocean worlds’ like Europa and Enceladus to have a correct and complete understanding of the geochemical and geological settings of these planetary bodies,” Mitra said. —