Mars’ ancient atmosphere probably didn’t have much oxygen after all
A new study finds that there may have been no oxygen in the atmosphere of ancient Mars — but don’t despair, organisms could still have crawled across the surface of the planet.
when nasa Curiosity roaming I found manganese oxide At the Martian rocks in 2016, many planetary scientists rejoiced, believing the presence of the mineral was an important hint at past oxygen concentrations in the planet’s atmosphere. Probabilities of life in the past Mars Suddenly it seemed higher, too, since oxygen is one of the main factors that enables life Land.
However, a new study based on laboratory experiments concludes that not only were high concentrations of oxygen necessary for the formation of minerals, but that the composition expected for antiquity Mars atmosphere It would have prevented oxygen-dependent reactions in the first place. Instead, the scientists said, abundant amounts of manganese oxide could have formed on Mars simply in the presence of halogen elements, such as chlorine and bromine, which are present on the Red Planet in greater quantities than those on Earth.
Related: Curiosity Rover: 15 amazing photos of Mars (gallery)
“Oxidation does not entail the sharing of oxygen by definition,” said Kaushik Mitra, a planetary geochemist at Stony Brook University in New York who led the study as part of his graduate research work at Washington University in St. Louis. statment (Opens in a new tab).
Oxidation is a chemical reaction in which a molecule or atom loses electrons. The reaction does not necessarily involve oxygen, but in many cases it leads to the formation of oxides, such as manganese oxide found on Mars.
“Earlier, we suggested viable oxidizers on Mars, other than oxygen or via ultraviolet radiation [ultraviolet] Photooxidation, he said, helps explain why the planet is so red, and added: “In the case of manganese, we haven’t had a viable alternative to oxygen that could explain manganese oxides until now.”
Kaushik and his collaborators were inspired by observations of the reactions that occur during the chlorination of drinking water, which involves adding chlorine-containing molecules to the water to kill microorganisms through oxidation. The researchers decided to test whether oxidation could occur in the halogen-rich environment on Mars. In the lab, they created samples of water with a composition similar to what might have been present on ancient Mars. The researchers said in the statement that when they immersed fragments of manganese minerals in water, scientists discovered that manganese quickly dissolved, forming manganese oxide thousands to millions of times faster than the presence of oxygen.
The scientists determined that the key to this amazing rate of oxidation was that the water contained chlorates and bromates, which are forms of the chlorine and bromine halogens common on Mars. Bromate was particularly effective at converting manganese into manganese oxides, enabling the reaction to proceed at a rapid pace. This was true even when the water samples contained high concentrations of carbon dioxide, which prohibits the formation of manganese oxides in the presence of oxygen alone.
This discovery is the key to disproving the theory about the abundance of oxygen in the Martian atmosphere that emerged after the discovery of Curiosity. Scientists also believe that the atmosphere of ancient Mars was rich in carbon dioxide, so because carbon dioxide prevented reactions with oxygen, the idea that the formation of manganese oxides required high concentrations of atmospheric oxygen no longer contained water.
“The association between oxides of manganese and oxygen suffers from a set of fundamental geochemical problems,” Jeffrey Catalano, a geochemist at Washington University, St. Louis, and corresponding author of the study, said in the release. “The halogens are present on Mars in different forms than they are on Earth, and in much greater quantities, and we guessed that they would be important to the fate of manganese.”
However, scientists stress that although oxygen may not have been present in the ancient atmosphere of Mars, the planet still teemed with the microscopic life forms of the past.
“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.”
studying (Opens in a new tab) Published Thursday (December 22) in the journal Nature Geoscience.
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