Ancient Mars may have been wetter and more geologically active than current surface images suggest, as a new study has revealed evidence of rocks in Jezero Crater being exposed to water in three different phases, one of which involved hot groundwater swirling inside the rocks.
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The researchers reached this conclusion after analyzing more than 185 rock targets in the "Margin Unit" region using the SuperCam instrument aboard the Perseverance rover, which landed in Jezero in February 2021 as part of a mission launched in July 2020.
The result is significant because it provides a more complex record of ancient water, information that helps scientists understand Mars' climate and its past habitability.
When the Perseverance rover arrived at the Margin Unit in September 2023, scientists expected to find sedimentary rocks formed on the shore of an ancient lake that once filled Jezero Crater. Instead, the rover found igneous rocks that originated from molten material deep within Mars or from volcanic activity.
By measuring the composition of rocks, SuperCam revealed that water had left its mark on them at different times. The instrument can analyze rocks remotely by shining a laser on them from a distance of up to 6.5 meters, then studying the resulting light to determine their chemical composition.
A more complex water record
In the first stage, groundwater rich in carbon dioxide reacted with the olivine mineral in the rocks, forming carbonate minerals within the cracks. The second stage is likely linked to the waters of an ancient lake, as scientists have found silica in rocks that lay below the lake's water level.
Eleni Ravanis, a planetary scientist at the University of Hawaii at Manoa and one of the study's authors, says that the transformation of olivine into carbonates can leave behind silica, which explains its increased presence in rocks that were submerged in water.
Fluorite is a significant indicator because it typically forms when hot water circulates through volcanic rock, suggesting hydrothermal activity beneath the Martian surface. "Mars constantly surprises you," says Purdue University researcher Candice Bedford, lead author of the study, noting that the rover's findings did not align with scientists' expectations based on orbital data.
What do the rocks of Mars tell us?
Researchers are not yet able to determine when each water event occurred, but they have been able to determine its order: first with groundwater rich in carbon dioxide, then lake water or changes in groundwater, and then hot thermal fluids at a later stage.
This makes the margin more like an intersection of different water systems, rather than simply the shoreline of an ancient lake as previously thought. Bedford believes these findings could help reconstruct the history of water, climate change, and early Mars habitability.
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