Curiosity rover discovers Earth-like past on the Red Planet

Rock samples at the bottom of an ancient, long-dry lake on Mars, examined by NASA's Curiosity rover, have revealed potentially habitable conditions billions of years ago.

A team of scientists, using the ChemCam instrument on board Curiosity, found higher than usual amounts of manganese oxide in the rocks of the Gale Crater lake on the Red Planet, a metal that is usually found in lakes on Earth due to its high oxidation conditions, which causes the formation of... Manganese crystals in the presence of oxygen.

The discovery of manganese in large quantities indicates that the sediments formed in a river, delta, or near the shore of an ancient lake, which means that similar ground conditions may have continued in Gale Crater, when it was filled with water in past eras.

“Manganese oxide is difficult to form on the surface of Mars, so we did not expect to find it in such high concentrations in beach sediments,” said Patrick Gasda, a geochemist and member of the Space Sciences and Applications Group at Los Alamos National Laboratory.

He continued: “On Earth, these types of deposits occur all the time due to the high percentage of oxygen in our atmosphere that is produced by photosynthetic life, and from microbes that help catalyze manganese oxidation reactions. On Mars, we have no evidence of the existence of life, and the mechanism of oxygen production.” "It's unclear how manganese oxide formed and was concentrated here in the ancient atmosphere of Mars. These results point to larger processes occurring on Mars." "The atmosphere or surface waters show that more work needs to be done to understand oxidation on Mars," he added.

Gasda and his colleagues studied manganese as analyzed by Curiosity's ChemCam instrument developed at Los Alamos Laboratory and the French Space Agency (CNES), which uses a laser to vaporize the mineral and then analyzes the light to determine its composition.

Next, scientists explored different mechanisms for manganese deposition in Gale Crater Lake: precipitation from lake water, or from groundwater through porous sand.

It is noteworthy that the sedimentary rocks explored by the vehicle are a mixture of sand, silt and clay.

Sandstone is more porous, and groundwater can more easily pass through sand than through the clay that makes up most of the lake-bottom rock in Gale Crater.

The team concluded that the most likely scenario is the deposition of manganese oxides along the lake shore in the presence of an oxygen-rich atmosphere. They say this is further evidence of a long-lived, habitable lake environment in ancient Gale Crater on Mars, where manganese oxide can take thousands of years to form, depending on oxygen levels.

However, the question of where this oxygen came from remains unanswered, although it is possible that meteorite impacts early in Mars' history could have released oxygen from surface ice deposits.

Oxidation by microbes may have left biological imprints and organic materials in the manganese-bearing rocks.

“The Gale Crater lake 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 Nina Lanza, principal investigator on the ChemCam team. “Manganese minerals are common in the shallow, oxidized waters found on "Lake shores on Earth, and it's amazing to find such distinctive features on ancient Mars."