An article published on Wednesday (1st) in the scientific journal Journal of Geophysical Research: Planets describes an intriguing discovery made by NASA’s Curiosity rover on Mars. In rocks in Gale Crater, the landing site of the robotic rover, a surprising amount of manganese oxide was detected.
This is a very common mineral in lakes on Earth, which presents highly oxidizing conditions, causing manganese crystals to form in the presence of oxygen. Its discovery on Mars in large quantities suggests that perhaps similar conditions persisted in Gale Crater when it was filled with water in the past.
“On Earth, these types of deposits happen all the time because of the high oxygen in our atmosphere produced by photosynthetic life and microbes that help catalyze these manganese oxidation reactions,” explains geochemist Patrick Gasda from the Laboratory in a statement. Los Alamos National – federal establishment belonging to the US Department of Energy, managed by the University of California.
Manganese on Mars is a mystery
According to Gasda, there is no evidence of life on Mars, and the mechanism for producing oxygen in the planet’s ancient atmosphere is unclear, “so how manganese oxide was formed and concentrated there is really intriguing.”
Common and abundant on Earth, manganese oxide is an essential mineral for several human biological processes, but virtually all life here requires manganese for one reason or another. There are even bacteria that depend on the oxidation states of manganese for energy, and their presence can accelerate the oxidation process.
There’s not much oxygen in Mars’ atmosphere right now, and we certainly haven’t found evidence of living bacteria, so it’s intriguing how manganese came to exist there in sedimentary rocks from coastal deposits in quantities comparable to an Earth-like environment.
Gasda and his colleagues did a thorough study of manganese analyzed by the Curiosity rover’s ChemCam, which uses a laser to vaporize minerals and then analyzes the light to determine their composition.
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The researchers explored different mechanisms for manganese precipitation in Gale Crater Lake: precipitation from lake water or groundwater through porous sands.
All mechanisms require the presence of highly oxidizing conditions, and after analyzing the options, they concluded that the most likely scenario would have been the precipitation of manganese oxides along a lakeshore in the presence of an oxygen-rich atmosphere.
According to the team, this is further evidence of a long-lived and habitable lake environment in ancient Gale Crater, as it could take thousands of years for manganese oxide to form, depending on oxygen levels.
Where did all the oxygen come from?
Where this oxygen came from is another question that remains unanswered, although it is possible that meteorite impacts early in Mars’ history may have released the element from surface ice deposits.
Microbe-mediated oxidation may have left biosignatures and organics in the manganese-bearing rocks. NASA’s Perseverance rover, which is currently exploring a dry delta environment, could look for them on its expeditions, according to researchers.
“The Lake Gale environment, as revealed by these ancient rocks, gives us a window into a habitable environment that looks surprisingly similar to places on Earth today,” says planetary scientist Nina Lanza of Los Alamos National Laboratory.
