In May 2017, NASA’s Curiosity rover observed higher than usual amounts of manganese in the lakebed rocks within Gale crater, Mars. These sedimentary rocks have larger grain sizes than what is typical for the lakebed rocks in the crater. This may indicate that the original sediments were formed in a river, delta, or near the shoreline in the ancient lake. In a new paper, Dr. Patrick Gasda from Los Alamos National Laboratory and his colleagues discuss how manganese could have been enriched in these rocks — for example, by percolation of groundwater through the original sediments or through the rock afterward — and what oxidant could be responsible for the precipitation of manganese in the rocks. On Earth, manganese becomes enriched because of oxygen in the atmosphere and this process is often sped up by the presence of microbes. Microbes on Earth can use the many oxidation states of manganese as energy for metabolism; if life was present on ancient Mars, the increased amounts of manganese in these rocks along the lake shore would be a helpful energy source for life.
“It is difficult for manganese oxide to form on the surface of Mars, so we didn’t expect to find it in such high concentrations in a shoreline deposit,” Dr. Gasda said.
“On Earth, these types of deposits happen all the time because of the high oxygen in our atmosphere produced by photosynthetic life, and from microbes that help catalyze those manganese oxidation reactions.”
“On Mars, we don’t have evidence for life, and the mechanism to produce oxygen in Mars’ ancient atmosphere is unclear, so how the manganese oxide was formed and concentrated here is really puzzling.”
“These findings point to larger processes occurring in the Martian atmosphere or surface water and shows that more work needs to be done to understand oxidation on Mars.”
To measure manganese abundances in lakebed rocks within Gale crater, Dr. Gasda and co-authors used the ChemCam instrument onboard…
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