Ancient Mars did not have atmospheric oxygen, claims new research

Manganese oxidation impossible

The scientists further used this process to show that manganese oxidation would not have been possible in the carbon dioxide-rich atmosphere present on ancient Mars.

“The link between manganese oxides and oxygen suffers from an array of fundamental geochemical problems,” said Jeffrey Catalano, a professor of earth and planetary sciences in Arts & Sciences and corresponding author of the study. Catalano was further supported in his work by Kaushik Mitra, a postdoctoral research associate at Stony Brook University.

The study highlighted that Mars is home to many halogen elements such as chlorine and bromine. 

“Halogens occur on Mars in forms different from on the Earth, and in much larger amounts, and we guessed that they would be important to the fate of manganese,” Catalano said.

Catalano and his colleagues therefore conducted laboratory experiments using chlorate and bromate to oxidize manganese in water samples that mimicked fluids present on Mars’ surface in the ancient past.

“We were inspired by reactions seen during chlorination of drinking water,” Catalano said. “Understanding other planets sometimes requires us to apply knowledge gained from seemingly unrelated fields of science and engineering.”

The researchers found that the production of manganese oxide did not require the presence of oxygen and that overall oxygen is altogether incapable of forming these elements.

“Oxidation does not necessitate the involvement of oxygen by definition,” Mitra said. 

“Earlier, we proposed viable oxidants on Mars, other than oxygen or via UV photooxidation, that help explain why the red planet is red. In the case of manganese, we just did not have a viable alternative to oxygen that could explain manganese oxides until now.”

Life present?

The scientists did however emphasize that just because there was no atmospheric oxygen in the past, there wasn’t necessarily no life on the Red Planet.

“There are several 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 — only that there was probably no oxygen-based lifeforms.”

Many organisms can survive in a halogen-rich environment such as that found on ancient Mars.

“We need more experiments conducted in diverse geochemical conditions that are more relevant to specific planets like Mars, Venus, and ‘ocean worlds’ like Europa and Enceladus in order to have the correct and full understanding of the geochemical and geological environments on these planetary bodies,” Mitra said. 

“Every planet is unique in its own right, and we cannot extrapolate the observations made on one planet to exactly understand a different planet.”

The study was published today in the journal Nature Geoscience.

Abstract:

In situ rover investigations on Mars have discovered manganese oxides as fracture-filling materials at Gale and Endeavour craters. Previous studies interpreted these minerals as indicators of atmospheric oxygen on early Mars. By contrast, we propose that the oxidation of manganese by oxygen is highly unlikely because of exceedingly slow reaction kinetics under Mars-like conditions and therefore requires more reactive oxidants. Here we conduct kinetic experiments to determine the reactivity of the oxyhalogen species chlorate and bromate for oxidizing dissolved Mn(II) in Mars-like fluids. We find that oxyhalogen species, which are widespread on the surface of Mars, induce substantially greater manganese oxidation rates than O2. From comparisons of the potential oxidation rates of all available oxidants (including reactive oxygen species peroxide and superoxide), we suggest that the oxyhalogen species are the most plausible manganese oxidants on Mars. In addition, our experiments precipitated the manganese oxide mineral nsutite, which is spectrally similar to the dark manganese accumulations reported on Mars. Our results provide a feasible pathway to form manganese oxides under expected geochemical conditions on early Mars and suggest that these phases may record an active halogen cycle rather than substantial atmospheric oxygenation.