A new study has found that rocks in Mars’s Jezero Crater were exposed to water during three distinct stages, one of which involved hot groundwater circulating through the rocks’ interior. The findings suggest that ancient Mars may have been wetter and more geologically active than its surface appears today, while providing a complex record that can help scientists study its ancient climate and its former potential to support life.
Analysis of 185 rock targets in the margin unit
The researchers reached their conclusions after analysing more than 185 rock targets in an area known as the margin unit, using the SuperCam instrument mounted on the Perseverance rover. The rover landed inside Jezero Crater in February 2021, as part of a mission launched in July 2020 to explore the area’s geological and hydrological history.
Perseverance reached the margin unit in September 2023, amid scientific expectations that it would find sedimentary rocks formed on the shore of the ancient lake that once filled Jezero Crater. Instead, the rover found igneous rocks, originally formed from molten material inside Mars or as a result of volcanic activity, contradicting interpretations based on data gathered from orbit.
SuperCam measurements of the rocks’ composition showed that water had left traces in them at different times. The instrument can carry out remote analysis by firing a laser beam at rocks from a distance of up to 6.5 metres, then examining the light produced by the process to determine their chemical composition and identify the minerals they contain.
Groundwater and an ancient lake leave mineral traces
During the first stage, carbon dioxide-rich groundwater reacted with the olivine mineral in the rocks, leading to the formation of carbonate minerals inside fractures. Scientists probably linked the second stage to water from the ancient lake after detecting silica in rocks that had been below the lake’s water level.
Eleni Ravanis, a planetary scientist at the University of Hawaiʻi at Mānoa and one of the study’s authors, said that the transformation of olivine into carbonates can leave behind silica. This could explain the higher presence of silica in rocks that had been submerged, adding evidence to the record of successive water–rock interactions in the area.
Sulphate veins reveal hydrothermal activity
The third stage involved the discovery of mineral veins about 0.25 metres thick in the eastern part of the margin unit. The veins contain calcium sulphate and fluorite, a mineral considered an important indicator because it usually forms when hot water moves through volcanic rocks, suggesting that hydrothermal activity occurred beneath the Martian surface.
Candice Bedford, a researcher at Purdue University and the study’s lead author, said that “Mars constantly surprises you”, explaining that what Perseverance observed on the surface did not match what scientists had expected based on orbital data. The findings indicate that the margin unit was not merely the shore of an ancient lake, but an area where multiple water systems met during successive stages.
Researchers cannot yet determine when each water-related event occurred, but they have been able to establish the sequence of the stages. The process began with carbon dioxide-rich groundwater, followed by lake water or changes in the groundwater, and later by hot hydrothermal fluids moving through the rocks.
Bedford believes the findings could help reconstruct the history of water and climate change on Mars, and improve understanding of the early planet’s potential to support life. Carbonates and silica are particularly important because they can preserve indicators of the geological and environmental past, while water–rock interactions on Earth can produce environments suitable for some microorganisms.
However, detecting hot water does not prove that life once existed on Mars; it reveals instead the diversity of aquatic environments that warrant further study.
