NASA’s Perseverance rover has revealed that Mars’ Jezero Crater was shaped by at least three distinct episodes of water activity. Exploring the crater’s Margin Unit since September 2023, the rover discovered unexpected igneous rocks bearing carbonate and silica, reshaping scientific understanding of the Red Planet’s ancient aqueous systems and habitability.
When NASA’s Perseverance rover arrived at the inner edge of Mars’ Jezero Crater in September 2023, mission scientists anticipated finding sedimentary layers deposited by an ancient lake. Orbital data had previously detected strong signals of carbonate minerals in the area, known as the Margin Unit, which hugs the shoreline of a basin where rivers once fed water.
Instead of sedimentary silt and clay, the rover uncovered igneous rocks formed deep underground from cooling magma or via volcanic surface activity. That geological twist revealed an intricate history of water that interacted with the Martian landscape through multiple distinct events.
Decoding the Margin Unit with SuperCam
To examine the unexpected terrain, the rover utilized its mast-mounted SuperCam instrument. Stationed up to 21 feet away from targeted formations, the instrument fires a laser to analyze the mineralogy and chemistry of the resulting plasma based on reflected light. Across an elevation range of about 870 feet (265 meters) through the Margin Unit, Perseverance analyzed more than 185 bedrock targets.
Higher elevations revealed coarse-grained, crystalline rock dominated by olivine with virtually no trace of water alteration. Lower on the ancient lakebed, however, the rock appeared heavily transformed, featuring fractured olivine grains interspersed with silica. Those findings, detailed in research published in the journal Communications Earth & Environment, indicate that the location acted as a complex crossroads for various water systems rather than a simple lakeshore.
“Before we arrived at the Margin Unit, the main hypothesis — derived from orbital observations — was that the carbonate seen from orbit formed from interaction with the lake that existed in Jezero Crater,” said Candice Bedford, a research scientist at Purdue University in West Lafayette, Indiana, and the study’s lead author. “But now we know that this location became a sort of crossroads for aqueous systems. The Margin Unit findings are important because Jezero Crater sits inside one of the largest exposures of carbonate on Mars, so what we learn here reaches well beyond this crater.”
Candice Bedford, research scientist at Purdue University in West Lafayette, Indiana
Three Distinct Episodes of Martian Water
While researchers can determine the chronological sequence of water activity in the Margin Unit, establishing exact dates remains challenging.
- First Episode: Carbon-dioxide-rich groundwater reacted with olivine, producing ridges of carbonate minerals within bedrock fractures that now stand exposed as softer surrounding rock wears away.
- Second Episode: A later episode appears to have involved Jezero’s ancient lake, where silica can form when olivine reacts with water.
Turning olivine into carbonate can leave silica behind, and we see more of that silica in rocks that sat below the water line.
- Third Episode: Heated subsurface water circulated through the volcanic rocks in the eastern Margin Unit, leaving behind mineral veins containing calcium sulfate and fluorite.
On Earth, hydrothermal systems and carbonate-silica mineral environments frequently support microbial life and preserve traces of past organisms. Although the rover data did not detect direct evidence of life, the discovered minerals offer optimal conditions for locking in clues about early planetary habitability.
Implications for Future Exploration
The surprises uncovered in Jezero Crater highlight the limitations of relying solely on orbital observations.
“If there is one thing I have learned after 10 years working with Mars rovers, it is that Mars constantly throws surprises at you. 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, I hope it helps planetary scientists reconstruct the changing climate and habitability of early Mars.”
Candice Bedford, research scientist at Purdue University
