In May 2017, NASA's Curiosity rover observed higher-than-usual amounts of manganese in rock at the bottom of a lake in Gale Crater on Mars. These sedimentary rocks have larger grain sizes than are typical of lake bed rocks within craters. This may indicate that the original deposits formed near the shoreline of a river, delta, or ancient lake. In a new paper, Dr. Patrick Gasda of Los Alamos National Laboratory and his colleagues explore how manganese became concentrated in these rocks, for example by groundwater infiltration through the original sediments and subsequent rocks. This paper discusses how manganese is enriched and what oxidizing agents might be considered. Involved in the precipitation of manganese in rocks. On Earth, atmospheric oxygen concentrates manganese, and this process is often accelerated by the presence of microorganisms. Microorganisms on Earth can use various oxidation states of manganese as metabolic energy. If life existed on ancient Mars, the increased amount of manganese in these rocks along the lake shore would provide a beneficial energy source for life.
Mastcam mosaic from the Sol 1686 spacecraft location, looking behind the spacecraft (downhill) at the transition point between Sutton Island and the Brunts Point Murray member. Images from Solus 1685-1689 show dark manganese-rich sandstone and the sedimentary texture of nearby rocks. Dashed boxes within the larger mosaic are shown as insets along the bottom of the figure. The small red outline indicates the approximate location and extent of ChemCam observations. Throughout this transition region, dark-toned sandstone (likely rich in manganese, based on his ChemCam observations at three locations) overlies lighter-toned material. Insets from left to right: (a) Denning Brook, manganese-rich fine-grained dark-toned sandstone ChemCam observations; (b) and (c) Two light-toned blocks with a cross-layered texture, highlighted by yellow lines, at the top left of a large mosaic 6 m away from Denning Brook. (d) Dark-toned material (center of mosaic). (E1) Newport Ledge, (E2) Aegis Post 1685a, (E3) Sugarloaf Mountain, dark-toned sandstone laminated in three thin planes. Image credit: NASA/Caltech-JPL/MSSS.
“Manganese oxides are difficult to form on the surface of Mars, so we did not expect to find such high concentrations of manganese oxides in shoreline sediments,” Gasda said.
“This type of deposit occurs all the time on Earth due to high atmospheric oxygen concentrations produced by photosynthetic life and microorganisms that help catalyze manganese oxidation reactions.”
“Since there is no evidence of life on Mars and the mechanism for producing oxygen in Mars' ancient atmosphere is unknown, how manganese oxide formed and became concentrated here is very puzzling.”
“These findings point to larger processes occurring in the Martian atmosphere and surface water and indicate that further research is needed to understand Martian oxidation.”
To measure the abundance of manganese in rocks on the lake bed within Gale Crater, Dr. Gasda and his co-authors used the ChemCam instrument aboard NASA's Curiosity rover.
“ChemCam is an atomic emission spectrometer that uses laser-induced breakdown spectroscopy (LIBS) to quantify the elemental abundance present in a target,” they explained.
“ChemCam LIBS uses a pulsed laser that emits a 1,067 nm beam focused on targets up to 7 meters away from the rover, producing an analytical footprint of 350 to 550 μm.”
“Each laser pulse ablates and ionizes a small amount (nanograms to micrograms) of material.”
“The light emitted from the plasma formed by each laser pulse is collected by the ChemCam telescope, and the spectrum is recorded by an ultraviolet, violet, visible to near-infrared spectrometer.”
The sedimentary rocks explored by the Curiosity rover are a mixture of sand, silt, and mud.
Sandstone is porous, which allows groundwater to pass through the sand more easily than the mud that makes up most of the rock at Gale Crater's lake bed.
The researchers are wondering how manganese became concentrated in these sands (e.g., by groundwater infiltration into the sands of lake shores and delta estuaries) and what oxidants may have enriched the manganese in the rocks. We investigated whether it was involved in precipitation. .
On Earth, atmospheric oxygen concentrates manganese, and this process is often accelerated by the presence of microorganisms.
Microorganisms on Earth can use various oxidation states of manganese as metabolic energy. If life existed on ancient Mars, the increased amounts of manganese in these rocks along the lake shore would have provided a beneficial energy source for life.
“The Gale Lake environment revealed by these ancient rocks gives us a window into a habitable environment that is strikingly similar to places on Earth today,” said ChemCam Principal said Dr. Nina Lanza, a researcher at Los Alamos National Laboratory.
“Manganese minerals are commonly found in shallow oxygen-containing waters found on lake shores on Earth, but it is remarkable that such recognizable features were found on ancient Mars.”
team's paper Published in Geophysical Research Journal: Planets.
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PJ Gasda other. 2024. Manganese-rich sandstone as an indicator of water quality in an ancient oxygen lake in Mars' Gale Crater. JGR: Planet 129 (5): e2023JE007923; doi: 10.1029/2023JE007923
Source: www.sci.news
