Perseverance found rocks altered by water on at least three separate occasions

Carbonate ridges, silica deposits and a fat vein of fluorite sit in the same patch of Martian rock, and NASA says the combination records water arriving three times. Perseverance’s laser instrument examined more than 185 bedrock targets across about 870 feet of elevation in the Margin Unit of Jezero Crater, and the result, published September 21, 2026, was not what orbital data had led the team to expect.

Mission scientists had expected the unit, a band along the edge of an ancient lakeshore, to be made of sedimentary layers laid down by the lake. The rover found igneous rock instead.

Olivine-rich bedrock where lake sediment was expected

NASA’s Jet Propulsion Laboratory, in its write-up of the work, says the rocks “showed signs of having interacted with water on at least three separate occasions, with each encounter further altering their chemistry and appearance.” That sentence is NASA’s characterisation of the result, and it is the basis for the figure of three. The study was led by Candice Bedford, a research scientist at Purdue University. The wording is “at least” three, which marks the count as a floor set by the evidence the rover could read, not a ceiling on how often water reached the rocks.

The paper appears as volume 7, article 728 of the journal and lists more than a dozen contributors from NASA and international institutions. Its authors set out to learn what the rocks of the Margin Unit were made of and how water had changed them, using the chemistry that SuperCam reads from each target rather than the broad mineral maps that orbiters produce. That ground-level reading is what turned a lakeshore band into a three-stage record.

The orbital hypothesis was that the carbonate seen from space formed through interaction with the lake that once filled the crater. Bedford said, in the NASA account, that the main hypothesis was the lake, but that the rover instead found “a sort of crossroads for aqueous systems.” The Margin Unit sits inside one of the largest exposures of carbonate on Mars, which NASA gives as the reason the findings reach beyond this one crater.

Carbonate, silica and fluorite as the three episodes

The paper in Communications Earth & Environment, titled for lake- and groundwater-associated alteration of the olivine-rich Margin unit, names the sequence. Its abstract describes three main alteration episodes, and NASA’s summary lists them in order.

First, carbon-dioxide-rich groundwater moved through the olivine-rich rock and left carbonate in fractures, which later formed ridges as the surrounding rock eroded. The paper describes those fluids as neutral to alkaline. Second came a stage linked to the ancient lake or to changing groundwater chemistry, in which carbonate was remobilised and silica was deposited, with the silica especially common in rocks that sat below the old waterline.

The third episode was hotter. According to NASA, a late water event produced mineral veins at one location in the eastern part of the Margin Unit, about 10 inches (25 centimeters) thick, made of calcium sulfate and fluorite. The paper describes late-stage hydrothermal activity moving through fractures, and Bedford summarised it as evidence of “a later period of heated groundwater activity” in Jezero.

SuperCam’s 185 targets and what remains open

The mapping depends on SuperCam, the rover’s laser-equipped instrument, which fires at rock up to 21 feet away and reads the minerals from the plasma it makes. The abstract lists olivine, iron- and magnesium-rich carbonates, silica, fluorite, calcium sulfates and pyroxenes among the minerals identified, and reports that the higher-elevation rocks were only minimally altered while the lower ground showed the complex water-rock history.

That pattern is part of the argument that water did not simply fill a basin once. The coarse, crystalline olivine-rich rock formed from slowly cooled magma, according to Purdue’s description, and every water episode came afterward and left its own minerals on top of that igneous base. Sci.News notes co-author Eleni Ravanis of the University of Hawaii among the team, and Purdue’s account, reproduced by Astrobiology.com, adds Roger Wiens, SuperCam’s team lead, and campaign science lead Briony Horgan.

Order and timing of the lake stage remain unsettled. Accounts differ on whether the silica reflects a separate flood of lake water or the reworking of carbonate that was already in place, and the paper calls the unit a locality of astrobiological interest rather than a site of life. In Space.com’s coverage, Bedford said that it is very rare for things to be as expected from orbital data on Mars, and that remains the clearest summary of the Margin Unit. In the Purdue account, she added that after ten years of working with Mars rovers, the planet keeps throwing surprises at the people studying it.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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