NASA's Perseverance rover has uncovered evidence that Mars may have been significantly wetter and more geologically active in the past. This finding stems from an area known as the Margin Unit, located along the inner edge of Jezero Crater. Between October 8 and October 16, 2023, the rover gathered data suggesting at least three distinct episodes of water interaction with Martian rocks, including hot groundwater circulating beneath the ancient surface.
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The Margin Unit, identified through orbital observations, consists of igneous rocks formed from molten material rather than sedimentary rocks initially expected to be found along an ancient lake shoreline. This unexpected geology holds a detailed record of water activity. Candice Bedford, lead author of the study and a research scientist at Purdue University, explained that prior hypotheses indicated that carbonates observed from orbit were formed by interactions with lake water. The new findings suggest this area served as a crucial intersection for various water systems.
Researchers utilized the SuperCam instrument to analyze over 185 bedrock targets within the Margin Unit. They identified different episodes of water altering the rocks. The first episode involved carbon-dioxide-rich groundwater reacting with olivine, a mineral formed from cooled magma, producing carbonate minerals in rock fractures. The second episode was linked to Jezero's ancient lake, with some rocks containing silica formed through olivine's interaction with water, abundant in areas that were formerly submerged.
The third episode indicated hotter conditions, with mineral veins of calcium sulfate and fluorite forming, evidence of hot water circulation through volcanic rocks. On Earth, such hydrothermal systems can create conditions favorable for microbial life, making these Martian water systems particularly interesting for researchers studying the planet's past habitability.
While researchers can outline the sequence of these water interaction episodes, the precise timeline remains unclear. The findings imply that the Margin Unit was more than just an ancient lakeshore; it was a site of interaction among groundwater, surface water, and heated fluids, potentially preserving a complex record of Mars' environmental evolution.
"If there is one thing I have learned after 10 years working with Mars rovers, it is that Mars constantly throws surprises at you," Bedford remarked. "It is very rare that things are as we expect them to be from orbital data. I hope this work helps reshape how scientists view the history of water in Jezero Crater and across Mars, ultimately aiding in the reconstruction of early Mars' climate and habitability." The study was published on September 21 in the journal Communications Earth & Environment.