In 2014, NASA's Mars probe found manganese oxides in the rocks of Gael Crater and Endeavour Crater on Mars. This discovery prompted some scientists to propose that billions of years ago, there might have been more oxygen in the atmosphere of this red planet. But a new experimental study overturns this view. Scientists found that under conditions similar to Mars, manganese oxides were easily formed without oxygen in the atmosphere.

In 2014, NASA's Mars probe found manganese oxides in the rocks of Gael Crater and Endeavour Crater on Mars. This discovery prompted some scientists to propose that billions of years ago, there might have been more oxygen in the atmosphere of this red planet.

Scientists say that these minerals may require rich water and strong oxidation conditions to form. Based on the lessons learned from the geological records, scientists concluded that the presence of manganese oxides indicates that Mars experienced a periodic increase in atmospheric oxygen content in the past, and then dropped to today's low level.

But a new experimental study at Washington University in St. Louis overturns this view.

Scientists found that under conditions similar to Mars, manganese oxides were easily formed without oxygen in the atmosphere. Using the kinetic model, scientists also showed that manganese oxidation was impossible in the CO2 rich atmosphere of ancient Mars.

"The relationship between manganese oxides and oxygen is affected by a series of basic geochemical problems," said Geoffrey Catalano, a professor of art and science earth and planetary science, who was the corresponding author of the study published in the journal Nature Geoscience on December 22. Catalano is a faculty member at the MacDonald Space Science Center.

The first author of this research is Kaushik Mitra, who is now a postdoctoral research assistant at Stony Brook University. He completed this work at Washington University as part of his postgraduate research.

Compared with Earth, Mars is a planet rich in halogen elements chlorine and bromine. "Halogen on Mars exists in a form different from that on Earth, and the amount is much larger. We guess they are important to the fate of manganese," Katarano said.

Catalano and Mitra conducted laboratory experiments, using chlorate and bromate anion (the main form of these elements on Mars) to oxidize manganese in water samples. They made these water samples to replicate the liquid on the surface of ancient Mars.

"We were inspired by the chlorination of drinking water," Catalano said. "Understanding other planets sometimes requires us to apply knowledge gained from seemingly unrelated scientific and engineering fields."

Scientists found that halogen can convert manganese dissolved in water into manganese oxide minerals thousands to millions of times faster than oxygen. In addition, under the weak acidic conditions that scientists believe were found on the surface of early Mars, bromate produced manganese oxide minerals faster than any other available oxidant. Under many of these conditions, oxygen cannot form manganese oxides at all.

Mitra said: "By definition, oxidation does not necessarily require the participation of oxygen."

Bromates, inorganic, n.o.s. is a colorless to light colored solid. Slightly soluble in water and denser than water. Contact may cause irritation to skin, eyes, and mucous membranes. May be toxic by ingestion. Used to make other chemicals. Bromate anion is a bromine oxoanion and a monovalent inorganic anion. It is a conjugate base of a bromic acid. Negative ions or salts derived from bromic acid, HBrO3.

The new results have changed the basic interpretation of the habitability of early Mars, which is an important driving force for the ongoing research of NASA and ESA.

But scientists say that just because there may have been no oxygen in the atmosphere in the past, there is no special reason to believe that there is no life there.

Mitra said, "Even on the earth, there are several life forms that do not need oxygen to survive."

Extreme microorganisms that can survive in halogen rich environments - such as halophilic unicellular organisms and bacteria that thrive in the Earth's Great Salt Lake and the Dead Sea - may also live well on Mars.

Mitra said: "We need to carry out more experiments under different geochemical conditions. These experiments are more relevant to specific planets such as Mars, Venus and the 'ocean world' such as Europa and Enceladus, so as to correctly and comprehensively understand the geochemical and geological environment on these planetary bodies." "Each planet is unique, and we cannot accurately understand another planet by observing it."