Data gathered by NASA’s Perseverance rover shows that the Margin Unit inside Jezero Crater on Mars was shaped by volcanic rocks repeatedly altered by water, including an ancient system of circulating hot groundwater. The research, published on Monday, September 21, 2026, in the journal Communications Earth and Environment, challenges previous orbital assumptions that the area was primarily composed of sedimentary deposits left behind by a calm lake.
Scientists led by Purdue University established that the crater rim hosts olivine-rich igneous rocks that underwent at least three separate aqueous episodes over geological time. The unexpected volcanic origin and complex chemical alterations indicate that Jezero Crater served as an intersection for subsurface fluids, lake interactions, and deep hydrothermal systems rather than a simple shoreline.
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Laser analysis of bedrock reveals multiple liquid interactions
Researchers examined more than 185 bedrock targets across the Margin Unit using the SuperCam instrument mounted on the mast of the rover. SuperCam fires an infrared laser capable of vaporizing rock samples from a distance of up to 6.5 meters, or 21 feet, allowing spectrometers to analyze the resulting plasma and determine the precise chemical and mineralogical composition of the target surface.
The chemical readings revealed that the exposed formations originated from molten magma deep underground or volcanic eruptions, rather than accumulated lake mud. Following their formation, these igneous bodies remained exposed to recurring flows of Martian water that altered their original structure and deposited secondary minerals across fractures and cavities.
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“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, research scientist in the Department of Earth, Atmospheric, and Planetary Sciences at Purdue University and lead author of the study. “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.”
Three distinct water episodes documented in volcanic formations
Geological mapping from the rover data identified a clear succession of aqueous events preserved within the rock record of the Margin Unit:
- First episode: Underground water saturated with carbon dioxide reacted directly with olivine minerals in cooling magma, generating extensive carbonate deposits within structural rock fractures.
- Second episode: Surface water from Jezero Crater’s ancient lake or shallow aquifers interacted with the exposed formations, leaving behind concentrated layers of silica minerals.
- Third episode: A subterranean hydrothermal system circulated heated fluids through the volcanic rocks, forming mineral veins filled with calcium sulfate and fluorite in the eastern Margin Unit.
The discovery of the third phase holds major relevance for astrobiology and the study of planetary habitability. On Earth, hydrothermal environments driven by heated groundwater provide abundant energy and dissolved minerals capable of sustaining microbial ecosystems, making these Martian formations a prime target for investigating past biological potential.
“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 said. “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.”
Exploration timeline and geological setting in Isidis basin
Perseverance landed inside the 45-kilometer-wide Jezero Crater on February 18, 2021, tasked with investigating ancient environments and caching geological core samples for potential return to Earth. The landing zone sits northwest of the Isidis impact basin and adjacent to the volcanic province Syrtis Major, placing it within one of the densest known concentrations of carbonate minerals on the Martian surface.
The robotic vehicle navigated across the crater floor and reached the inner rim boundary known as the Margin Unit on September 1, 2023. Satellite sensors orbiting Mars had previously detected strong carbonate signatures throughout this perimeter band, leading geologists to anticipate typical lacustrine carbonates formed in shallow standing water before ground-level exploration confirmed their igneous foundation.
Dating limitations and remaining scientific questions
The research team has not yet determined the absolute geological age of each aqueous episode. While the relative stratigraphic sequence of the three events is established by mineral cross-cutting relationships, calculating the exact numerical dates when groundwater and hydrothermal fluids ceased flowing will require further isotopic analysis of samples collected by the mission.
