When NASA’s Mars rover found manganese oxides in rocks in the Gale and Endeavor craters on Mars in 2014, the discovery prompted some scientists to suggest that the red planet might have had more oxygen in its atmosphere billions of years ago.
The scientists said the minerals probably require abundant water and highly oxidizing conditions to form. Using lessons learned from Earth’s geological record, the scientists concluded that the presence of manganese oxides indicates that Mars experienced periodic increases in atmospheric oxygen in the past – before dropping to low levels today.
But a new pilot study from Washington University in St. Louis turns that view on its head.
Scientists have discovered that under Mars-like conditions, manganese oxides can easily form without oxygen in the atmosphere. Using kinetic modeling, the scientists also showed that oxidation of manganese is not possible in the carbon dioxide-rich atmosphere expected on ancient Mars.
“The association between oxides of manganese and oxygen suffers from a set of fundamental geochemical problems,” said Jeffrey Catalano, Professor of Earth and Planetary Sciences in Arts & Sciences and corresponding author of the study published Dec. 22. Natural Earth Sciences. Catalano is a faculty fellow at the McDonnell Space Science Center.
The first author of the study is Kaushik Mitra, now a postdoctoral researcher at Stony Brook University, who completed this work as part of his graduate research at the University of Washington.
Mars is a planet richer in the halogen elements chlorine and bromine compared to Earth. “The halogens are found on Mars in different forms than on Earth, and in much greater quantities, and we guessed that they would be important to the fate of manganese,” said Catalano.
Catalano and Mitra conducted lab experiments using chlorates and bromates—the dominant forms of these elements on Mars—to oxidize manganese in water samples they made for fluid replications on Mars in the ancient past.
“We were inspired by the reactions seen during the chlorination of drinking water,” said Catalano. “Understanding other planets sometimes requires us to apply knowledge gained from seemingly unrelated fields of science and engineering.”
Scientists have found that halogens convert manganese dissolved in water into manganese oxide minerals thousands to millions of times faster than oxygen. Moreover, under the weakly acidic conditions that scientists believe existed on early Mars, bromate produces manganese oxide minerals more rapidly than any other available oxidizer. Under many of these conditions, oxygen is completely unable to form manganese oxides.
“Oxidation does not require the interference of oxygen by definition,” Mitra said. “Earlier, we suggested viable oxidizers on Mars, other than oxygen or via ultraviolet photooxidation, that help explain why the Red Planet is red. In the case of manganese, we had no viable alternative for oxygen that could explain manganese oxides yet. “
The new findings change foundational interpretations of the habitability of early Mars, an important driver of ongoing research by NASA and the European Space Agency.
The scientists said that just because there was no oxygen in the atmosphere in the past, there is no particular reason to believe there was no life.
“There are many life forms even on Earth that do not require oxygen to survive,” Mitra said. “I don’t think of it as a ‘setback’ to habitability — just that there probably are no oxygen-based life forms.”
Extreme organisms that can survive in a halogen-rich environment — such as the single-celled salt-loving organisms and bacteria that thrive in Earth’s Great Salt Lake and Dead Sea — could also do well on Mars.
“We need more experiments conducted in diverse geochemical conditions more relevant to specific planets such as Mars and Venus and ‘ocean worlds’ such as Europa and Enceladus in order to obtain a correct and complete understanding of the geochemical and geological environments on these planets,” Mitra said. se, and we can’t extrapolate from observations made on one planet to understand a completely different planet.”
Jeffrey Catalano, Formation of Manganese Oxides in Early Mars Due to the Active Halogen Cycle, Natural Earth Sciences (2022). DOI: 10.1038/s41561-022-01094-y. www.nature.com/articles/s41561-022-01094-y
Provided by Washington University in St. Louis
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