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In a Nutshell
- Rock once thought to be ancient lake shore sediment turns out to be mostly solidified volcanic material that formed underground, not on a beach.
- Scientists found evidence of three separate episodes where water or watery fluids moved through the rock at different times, each leaving behind different minerals.
- This layered water history strengthens the case that this part of Mars is a strong candidate for preserving signs of ancient life.
A stretch of Martian ground once thought to have formed along an ancient lakeshore turns out to be mostly solid rock that cooled slowly from magma, even if parts near the shore were later shuffled around by the lake. It only took on its watery, lakeshore-like character after fluids worked their way through it in at least three separate waves. That is the surprising picture NASA scientists have pieced together about a strip of rock on Mars once considered one of the best places in the solar system to search for signs of ancient life.
Since 2021, NASA’s Perseverance rover has been rolling around Jezero Crater, a 45-kilometer-wide bowl on Mars that once held a lake. Orbiting spacecraft had spotted a puzzling band of rock along the crater’s edge, nicknamed the “Margin unit,” that seemed to carry the chemical fingerprints of a lake’s edge, the kind of spot where minerals settle out of standing water and where traces of ancient life, if Mars ever had any, might still be preserved. That idea made the Margin unit a top target for the rover’s cameras, lasers, and drills.
New results from the mission, published in the journal Communications Earth & Environment, tell a different story. Rather than being lake sediment through and through, most of the rock appears to have started out as a chunk of slowly cooled volcanic material packed with a greenish mineral called olivine, the same mineral that forms deep inside cooling magma on Earth. Water came later, and not just once. Scientists identified three separate waves of fluid moving through the rock over time, each leaving its own chemical mark. That layered history, the research team says, makes the Margin unit an even richer target in the search for ancient life than scientists first thought.
How the Perseverance Rover Pieced Together Mars Rock’s Watery Past
Perseverance carries an instrument called SuperCam, mounted on the rover’s mast, which can zap rocks with a laser from several feet away without needing to drive up and touch them. The zapped material briefly turns into a glowing cloud of charged gas, and the light it emits reveals which chemical elements are present. SuperCam also snaps close-up pictures of rock surfaces and can pick out certain minerals using other light-based tricks. Using this instrument, researchers studied more than 185 rock targets scattered across the Margin unit as the rover traveled through four sections, informally named East, West, North, and High Margin.
Rock examined at the highest elevations looked and behaved like it had cooled slowly from magma, with tightly interlocking mineral grains and little sign of ever having been soaked by water. That section sits above where scientists believe the ancient lake’s water line once stood. Lower down, in areas that would have sat beneath the lake’s estimated high-water mark, the story changed. Rock there showed clear signs of alteration by fluid moving through cracks and small pores, along with evidence of physical wear near a channel called Neretva Vallis and a nearby fan-shaped feature.
Digging into the chemistry, the team grouped the data by shared mineral patterns and matched those groups to textures visible in the rover’s images. That approach let them reconstruct a rough timeline. First, fluids that were not too acidic and carried dissolved carbon dioxide moved through cracks in the original rock, leaving behind carbonate minerals, which typically need water to form. When the softer rock around those cracks wore away over time, the carbonate-filled cracks stuck out as raised ridges, still visible today across the East and West Margin sections. Second, either the lake itself or shifting underground water changed conditions enough to dissolve some of that carbonate and deposit a glassy mineral called silica in the empty spaces left behind. Third, and latest in the sequence, hot mineral-rich fluids pushed through younger cracks and left behind veins containing calcium sulfate and a mineral called fluorite.
One of the study’s more surprising comparisons involves a different chunk of crater-floor rock called the SĂ©itah formation, which sits lower in the crater and, by the researchers’ reasoning, should have been just as exposed to the ancient lake. Yet SĂ©itah shows far less water alteration than the Margin unit. The team suggests this might be because SĂ©itah lacked the same network of cracks that would have let water seep in and react with the rock. In other words, cracks in the rock, not just contact with lake water, decided how much alteration a given rock experienced.
Three core samples were collected across the Margin unit, named Pelican Point, Lefroy Bay, and Comet Geyser, for a possible future mission that would bring Martian rock samples back to Earth for study in laboratories.
Why This Mars Discovery Matters for the Hunt for Ancient Life
None of this changes the basic reason the Margin unit mattered in the first place. Multiple episodes of water moving through cracked, mineral-rich rock can trap and preserve chemical evidence, since each pulse of fluid could have carried and locked away something different. As the researchers put it, this sequence of fluid events “reinforces the Margin unit as a locality of astrobiological interest.” The rock did not need to be old beach sediment to be scientifically exciting. It needed water to pass through it more than once, in more than one way, and the data now shows exactly that. The samples already sitting in Perseverance’s collection tubes may eventually let scientists on Earth check whether any of those ancient fluids left behind more than just minerals.
Paper Notes
Limitations
Researchers note several open questions in their analysis. The heavily altered rock in the East and West Margin sections made it harder to pin down the rock’s original texture and origin, since water exposure had reworked much of the evidence. A large mineral vein called Point Cloates had an uncertain relationship to the surrounding bedrock because loose surface debris partly covered it, though images from other rover cameras suggested it extended well beyond what is visible at the surface. The exact process that formed the fluorite-bearing mineral veins remains unknown, since the area lacks obvious volcanic features that would typically explain such formations on Earth. The team also could not fully explain why the SĂ©itah formation shows much less water alteration than the Margin unit despite sitting in a similarly low position in the crater, though they propose that a lack of fractures may have limited water movement there.
Funding and Disclosures
Several authors acknowledged support from NASA’s contract for the SuperCam instrument. Other authors reported funding from Spain’s Ministerio de Ciencia e InnovaciĂ³n and European Regional Development Fund support through a project called PAMMAT, a postdoctoral fellowship from the Centre National d’Études Spatiales in France, an Imperial College London President’s PhD Scholarship, and funding tied to NASA’s Mars 2020 Project through a subcontract involving Arizona State University. The authors stated they have no competing interests as defined by Nature Portfolio. One author, Candice C. Bedford, is an editorial board member for the journal Communications Earth & Environment but was not involved in the editorial review or the decision to publish this article.
Publication Details
Paper Title: “Lake- and groundwater-associated alteration of the olivine-rich Margin unit in Jezero crater, Mars”
Journal: Communications Earth & Environment (2026, volume 7, article 728)
Authors: Candice C. Bedford, with coauthors Eleni Ravanis, Roger C. Wiens, Elise Clavé, Julene Aramendia, Juan Manuel Madariaga, Eleanor Moreland, Stephanie Connell, Alexander Jones, Briony Horgan, Olivier Forni, Bradley Garczynski, Susanne Schröder, Kenneth Williford, Linda Kah, Kathryn Stack, Lucia Mandon, Agnés Cousin, Pierre Beck, Erwin Dehouck, Clément Royer, and Adrian Brown
