Rocks remember water even after it's gone. That's the premise behind a new study of Jezero Crater's "Margin unit" — a rind of olivine-rich terrain hugging the crater's rim — which finds not one but three separate chapters of water-rock interaction stacked into the same stretch of Martian bedrock. The paper, published September 21, 2026 in Communications Earth & Environment, was led by Candice C. Bedford of Purdue University with 21 co-authors, including Eleni Ravanis, Roger C. Wiens, and Briony Horgan, drawing on laser-spectroscopy data collected by NASA's Perseverance rover.
Perseverance first reached the Margin unit in September 2023 and has since climbed roughly 870 feet (265 meters) of elevation across it, pausing along the way to zap target after target with its SuperCam instrument — a rock-vaporizing laser that can fire from as far as 21 feet (6.5 meters) away and read the resulting spark for chemical and mineral fingerprints. Across the traverse, the team built a dataset from more than 185 bedrock targets, enough to start sorting individual mineral veins and ridges into a timeline rather than treating them as one undifferentiated smear of alteration.
Three Episodes, Written in Stone
That timeline, as the paper lays it out, runs in three acts:
First, neutral-to-alkaline, carbon-dioxide-rich fluids moved through the rock and precipitated carbonate minerals, building up the carbonate-rich ridges that make the Margin unit so distinctive in orbital data. Second, a later episode — tied to a possible paleolake or groundwater system — remobilized some of that carbonate and left silica behind in its place. Third, in the last of the three episodes, hot hydrothermal fluids pushed through younger fractures in the rock and deposited veins of fluorite-bearing calcium sulfate; one such vein, in the eastern part of the Margin unit, measured about 10 inches (25 centimeters) thick.
Layering three chemically distinct fluid systems onto one rock unit means Jezero's rim didn't just get wet once. It got wet, dried out or shifted chemistry, got wet again in a different way, and then — potentially much later — was invaded by hydrothermal fluids that had nothing to do with a lake at all. Reconstructing that sequence required distinguishing which minerals cut across which fractures, essentially rock stratigraphy read one laser shot at a time.
The View From Purdue
"The Margin Unit findings are important because Jezero Crater sits inside one of the largest exposures of carbonate on Mars," Bedford said in a statement accompanying the paper. Carbonate matters to Mars scientists for two reasons: it forms in the presence of water and it's good at preserving organic material and other biosignatures.
Ravanis, a co-author based at the University of Hawaii, pointed to the silica component of the second episode — noting it was found below what appears to be the crater's historic water line, consistent with a lake or groundwater system reworking the rock's chemistry at that elevation. That detail helps anchor the middle chapter of the three-part sequence to an actual body of water rather than a more diffuse groundwater process alone.
Why It Matters
None of this proves Mars once hosted life. What it does is narrow the search for evidence, if any exists, to specific minerals formed under specific conditions at specific points in time. Carbonate-forming groundwater, a paleolake stage, and late hydrothermal veining are each associated on Earth with environments that can preserve or generate biosignatures — carbonates trap organics, silica is an excellent preservation medium, and hydrothermal systems can concentrate minerals and, in some Earth analogs, sustain microbial communities far from sunlight. Finding all three stacked in one accessible outcrop gives scientists multiple distinct targets to weigh, rather than a single ambiguous rock type.
It also sharpens the case for the samples Perseverance has already cached. The rover has been collecting cores as it traverses, with the expectation that a future sample-return mission will eventually bring them to Earth. A three-stage alteration history means those cached cores from the Margin unit aren't just "old rock that touched water once" — they potentially represent three different water chemistries and three different windows in time, each with its own preservation potential for biosignatures, assuming any existed to preserve.
Reception
The paper has drawn attention quickly. As of September 22, 2026 — the day after publication — its Altmetric Attention Score placed it in the top 5% of all tracked research outputs, ranking in the 97th percentile for papers of its age, according to the study's Altmetric page. That's an unusually fast uptake for a planetary geochemistry paper, reflecting both the ongoing public interest in Perseverance's search for signs of ancient life and the significance of pinning down a multi-stage water history in one of the mission's most carefully studied units.
The Margin unit work is a reminder that the most interesting results from Mars exploration often aren't single dramatic discoveries but patient reconstructions — laser shot by laser shot, vein by vein — of processes that played out over enormous stretches of time before any rover existed to observe them.
