Perseverance finds signs hot water once flowed through the rocks of Jezero Crater

Mineral veins packed with calcium sulfate and fluorite, found in a band of olivine-rich rock inside Jezero Crater, are the newest evidence that hot water once moved through the Martian bedrock. NASA’s Perseverance rover read the veins with its laser-based SuperCam instrument, and a team led by Candice Bedford of Purdue University reported the result on September 21 in the journal Communications Earth & Environment.

The veins are only the last chapter of the story the paper tells. Rocks in the Margin Unit, the rim-hugging layer that orbiters flagged years ago as rich in carbonate, turned out to record three separate episodes of water and rock reacting, each under different conditions.

Three episodes in one band of rock

The paper, titled Lake- and groundwater-associated alteration of the olivine-rich Margin unit in Jezero crater, Mars, describes the sequence in order. First came “neutral-to-alkaline CO2-rich fluids” circulating through the bedrock and building carbonate-rich ridges. Later, water tied to the ancient lake or to groundwater dissolved and moved some of that carbonate and left silica behind in pore spaces.

The third episode is the source of the hot-water claim. Younger fractures in the rock host “fluorite-bearing, Ca-sulfate mineral veins,” which the authors read as late-stage hydrothermal activity, meaning warm to hot fluid circulating underground. The paper does not pin the veins to a specific temperature, so the word hot rests on the minerals and the setting rather than on a thermometer reading. Space.com’s coverage describes the veins as forming in the eastern part of the Margin Unit.

Olivine matters to the first two episodes. According to Space.com, carbon-dioxide-rich groundwater reacted with olivine minerals to make the carbonates found in rock fractures, and olivine-water reactions also produced silica, particularly in rocks below the ancient lake’s waterline. In other words, the same volcanic mineral supplied the raw material for two different products, which is what let the team read separate water histories from one band of rock.

What SuperCam actually measured

The team analyzed more than 185 bedrock targets with SuperCam across the unit, according to Space.com, using observations collected on October 8 to 16, 2023. SuperCam fires a laser at a rock, reads the light from the resulting plasma and uses reflected light to identify minerals, which lets the rover survey outcrops it never touches. That reach is what allowed the authors to compare rocks at different elevations and tie each alteration episode to where it appears in the crater.

Bedford, a research scientist in Purdue’s Department of Earth, Atmospheric, and Planetary Sciences, said in the university’s announcement of the study that “the fractures are like pipes, and the carbonate is the Mars ‘limescale’ that eventually blocked the ‘pipes’ up.” The image fits the first episode, when carbonate-laden fluid moved through cracks and left minerals behind in them.

Contributors named by Purdue include Roger Wiens, the SuperCam lead, and Briony Horgan, campaign science lead, along with former doctoral students Stephanie Connell and Brad Garczynski. A separate EurekAlert release dated September 22 lists the paper’s DOI as 10.1038/s43247-026-03997-9.

Open questions remain about the veins. Neither the paper’s abstract nor the coverage of it gives a temperature for the water, so how hot it ran, how long it flowed and how it relates in time to the lake that later filled the crater are not settled by this dataset. Those gaps are typical of orbital-to-rover comparisons, where a mineral list can be read confidently and a thermometer cannot. Future rover targets and any returned samples would be the natural tests, since laboratory instruments can date and temperature-calibrate vein minerals in ways a laser on a mast cannot.

Why hot water matters for habitability

Warm water moving through fractured volcanic rock is a familiar setting for life on Earth, where hydrothermal systems support communities of microbes that live on chemical energy. The Space.com report says the findings point to overlapping groundwater, surface-water and hydrothermal systems on ancient Mars, any of which could have offered habitable niches. The paper itself calls the Margin unit “a locality of astrobiological interest” because such conditions may preserve biosignatures.

Bedford told Space.com that “Mars constantly throws surprises,” a reference to how often the rover’s close-up view departs from what orbital data suggested. The Margin Unit fits that pattern: instruments in orbit saw carbonate, but only the rover could show that the carbonate sits in a stack of altered layers with a hydrothermal ending.

Perseverance landed on February 18, 2021, in Jezero Crater, a 28-mile-wide basin chosen because it once held a lake, according to NASA’s mission page. Its samples are being cached for a possible return to Earth, and the Purdue team says the alteration history will help guide how any returned rocks are studied. Whether a carbonate-bearing core from the Margin Unit ever reaches a laboratory remains an open question.

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

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