New data from NASA’s Perseverance rover have revealed that the Margin Unit, located on the inner rim of Jezero Crater, has experienced a much more complex history of interaction with water than scientists previously thought based on orbital observations. Researchers initially expected to find sedimentary rocks left behind by an ancient lake. However, Perseverance discovered evidence of at least three different episodes in which water interacted with igneous rocks formed from volcanic activity.
In the upper part of the Margin Unit, about 265 meters above the lowest areas of the region, Perseverance detected coarse-grained rock containing olivine with very few signs of water exposure. Its structure suggests that magma cooled slowly deep beneath the Martian surface before moving upward. Further down the slope, however, the olivine crystals had been altered.
The spaces between them were filled with silica, while carbonates and other silicate minerals were also found in the rocks. On Earth, when olivine comes into contact with water, it can produce hydrogen, which can serve as a potential source of energy for microorganisms. This makes such minerals particularly interesting in the search for possible signs of ancient microbial life on Mars.
Scientists believe that one stage of this process involved groundwater rich in carbon dioxide. The water entered cracks in the olivine-rich rocks and triggered chemical reactions that eventually led to the formation of carbonates. A second episode may have been connected with the ancient Lake Jezero or with changes in the composition of underground water.
During this period, some of the carbonates were redistributed, while silica accumulated in tiny spaces within the minerals. So far, Perseverance has examined more than 185 bedrock outcrops using its SuperCam instrument. The instrument can fire a laser at rocks, vaporize a tiny amount of material, and analyze the resulting plasma from a distance of up to 0.5 meters.
This allows scientists to study the chemical composition of Martian rocks without having to drill into every sample. The third sign of water activity appears to be connected with hot hydrothermal fluids. In the eastern part of the Margin Unit, researchers discovered mineral veins about 25 centimeters thick containing calcium sulfate and fluorite.
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