The Curiosity Mars rover has detected intriguing chemical proof, within the type of anomalous quantities of manganese oxide, which factors to Mars having had not solely a liveable atmosphere billions of years in the past, but in addition one presumably inhabited by microbes.
NASA’s Curiosity is exploring the large 154-kilometer (about 96-mile) diameter Gale crater, the place the rover landed in 2012. Curiosity’s discoveries have already established that the crater was a minimum of partially flooded way back, though the proof for this has been contested. Nonetheless, the rover’s newest findings not solely strengthen the argument for an historic lake, but in addition recommend that situations throughout the lake had been conducive to life.
The proof is related to the compound manganese oxide. Curiosity first discovered small portions of manganese oxide in Gale Crater in 2016, however now it has found a lot better abundances of manganese oxide in sedimentary bedrocks of a mudstone geological unit referred to as the Murray Formation. The Murray Formation is discovered on the flank of Mount Sharp in the course of the crater.
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The manganese oxide was recognized by Curiosity’s ChemCam instrument, which fires a laser at rocks that scientists want to examine. The laser heats a small patch of a rock’s floor, thereby vaporizing it, which leads to a small cloud of plasma that ChemCam’s onboard digicam and spectrometer can examine from a distance to find out the ablated materials’s composition. ChemCam found mudstone that was enriched in manganese oxide by as much as 45%.
On Earth, manganese oxide is usually present in lakebeds or river deltas the place there are excessive oxidizing situations. Moreover, microbes that exist in these environments are in a position to assist catalyze the oxidation course of.
Normally, this course of requires a gentle stream of oxygen, which is in brief provide on Mars. The beforehand found small quantities of manganese oxide discovered on Mars in 2016 could be defined with out vital portions of oxygen, however the massive abundances found within the Murray Formation are one other matter solely. To achieve such abundances, the oxidation course of would require a big quantity of oxygen.
“It’s troublesome for manganese oxide to kind on the floor of Mars, so we did not anticipate finding it in such excessive concentrations in a shoreline deposit,” mentioned lead researcher Patrick Gasda of the Los Alamos Nationwide Laboratory in a assertion. “On Mars, we do not have proof for all times, and the mechanism to provide oxygen in Mars’ historic environment is unclear, so how the manganese oxide was fashioned and concentrated right here is de facto puzzling.”
One clue is within the nature of the mudstone sediments that the manganese oxide was present in. The rocks enriched in manganese oxide had been discovered at a location between two geological models within the Murray Formation. One unit is nicknamed Sutton Island and appears to symbolize sediments laid down on the fringe of a lake; the opposite, nicknamed Blunts Level, would have been deeper within the lake.
The manganese-oxide-enriched mudstone is coarser, with bigger grains than bedrock elsewhere within the crater the place solely small abundances of the compound have been found. This helps the idea that the Sutton Island/Blunts Level area is both the location of an historic river delta that when emptied into the lake, or a shoreline of the lake, each of which symbolize places the place larger-grained sediments would have been preferentially laid down. The bigger grains would have contributed to forming a extra porous bedrock than the fine-grained mudstone seen elsewhere in Gale Crater — mudstone that’s presumably from a lot deeper within the lake. This porosity would have allowed groundwater to cross by extra freely. The manganese may have percolated out of this groundwater because it handed by the coarse-grained mudstone, the scientists say, thus changing into concentrated throughout the rocks. The place the oxygen got here from to oxidize it, nonetheless, stays a puzzle.
“These findings level to bigger processes occurring within the Martian environment or floor water and present that extra work must be finished to know oxidation on Mars,” mentioned Gasda.
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The presence of manganese oxide additionally bolsters the chance that microbial life may have existed throughout the lake. Not solely can microbes catalyze the oxidation of manganese, however they’re additionally probably in a position to make use of manganese’s many oxidation states as a supply of chemical vitality for his or her metabolisms, as microbes do on Earth. In different phrases, in a approach, the abundance of manganese oxide is maybe an oblique biosignature.
“The Gale lake atmosphere, as revealed by these historic rocks, offers us a window right into a liveable atmosphere that appears surprisingly much like locations on Earth right now,” mentioned Los Alamos’ Nina Lanza, who’s the Principal Investigator for ChemCam. “Manganese minerals are widespread within the shallow, oxic waters discovered on lake shores on Earth, and it is outstanding to seek out such recognizable options on historic Mars.”
The findings had been printed on Could 1 within the Journal of Geophysical Analysis: Planets.
