Perseverance finds groundwater, a lake and hot fluids all soaked the same Mars rock

The rocks NASA’s Perseverance rover drove to on the inner edge of Jezero Crater were supposed to be an ancient lakeshore. They turned out to be volcanic rock that water had soaked, dissolved and re-cemented at least three separate times: first carbon-rich groundwater, then the crater’s own lake, and finally hot fluids that pushed through fresh cracks and left veins of fluorite and calcium sulfate.

That sequence matters because each of those waters is a different kind of habitat. Groundwater seeping through olivine-rich rock, standing lake water and warm underground circulation are all environments where microbes thrive on Earth, and the Margin Unit, as this band of rock is called, recorded all three in one place. The team behind the study now describes the site as a crossroads of watery systems rather than a single shoreline.

Three cores of this rock are sealed in tubes inside the rover. Nobody has a funded plan to bring them home.

How SuperCam read 185 rocks from up to 6.5 meters away

The work rests on SuperCam, the instrument mounted on Perseverance’s mast about two meters above the ground. It fires a laser at a rock from as far as 6.5 meters, vaporising a spot a few tenths of a millimeter wide into a tiny burst of plasma. The light that plasma gives off as it cools reveals which elements are in the rock, and a second spectrometer reads minerals from reflected light. A small color camera photographs each spot so geologists can see grain size and texture.

Perseverance used that laser on more than 185 bedrock targets across the Margin Unit, climbing roughly 265 meters of elevation along the crater wall. Lead author Candice Bedford, a research scientist at Purdue University, and her colleagues sorted the results into chemical families and matched them to what the rocks looked like up close. They then mapped where each family appeared relative to the old water levels of the crater lake, which earlier studies had reconstructed from terraces visible from orbit.

That last step is what cracked the story. High up the slope, above about 2,350 meters below the Martian reference level, the rock is a slowly cooled, crystalline, olivine-rich body that shows little sign of water at all. Lower down, below the lake’s second terrace, the same rock is altered, fractured and filled.

Three waters in the same rock, in order

The first water came from below. Neutral-to-alkaline groundwater rich in carbon dioxide moved through fractures in the bedrock and reacted with olivine, a green volcanic mineral, depositing carbonate in the cracks. Erosion later stripped the softer rock around those fillings and left them standing as ridges. “The fractures are like pipes, and the carbonate is the Mars ‘limescale’ that eventually blocked the ‘pipes’ up,” Bedford said.

The second water was more acidic and probably cooler. It dissolved some of that carbonate, opened small pores in the rock and filled them with silica. The silica-rich rocks appear only in the parts of the Margin Unit that sat below the lake’s second shoreline, which is why coauthor Eleni Ravanis of the University of Hawaiʻi at Mānoa and the team link this stage to the lake itself, or to groundwater that had spent a long time reacting with rock.

The third water was hot. Late fluids flowed through younger fractures and precipitated a vein of calcium sulfate and fluorite about 25 centimeters thick. Fluorite can form in cold Martian groundwater as a trace mineral, but a vein that size looks like hydrothermal deposits on Earth. The authors point to a possible volcanic structure on the edge of Jezero and the nearby Syrtis Major volcanic province as the likely heat source.

Why a carbonate crossroads matters beyond Jezero

Jezero is a 45-kilometer crater that once held a lake fed by a river, and Perseverance was sent there because orbiters spotted carbonate along its rim. On Earth, carbonate and silica are among the best minerals at locking away chemical and microscopic traces of ancient life. A carbonate shoreline was the scenario that made this patch of crater wall a top target.

“Before we arrived at the Margin Unit, the main hypothesis was that these carbonates formed from interaction with the lake that existed in Jezero Crater, but now we know that this location became a sort of crossroads for aqueous systems,” Bedford said.

The finding also reaches past the crater. Jezero sits inside one of the largest exposures of carbonate on Mars, an olivine-rich layer that runs across the wider Nili Fossae region. Orbital spectra from outside the crater already looked similar to the Margin Unit, hinting at groundwater or hydrothermal origins there too. If the same story holds across that region, groundwater rather than open lakes may explain much of the carbonate seen from orbit.

There is one more reason astrobiologists care. When water reacts with olivine on Earth, the reaction can release hydrogen, a chemical fuel that some microbes live on. The rocks show that this kind of water-rock chemistry happened here, repeatedly.

What the rocks don’t settle yet

None of this is evidence of life. The study maps minerals and chemistry; it reports no organic molecules or biosignatures from the Margin Unit.

The method has limits. SuperCam’s laser measures elements in spots a fraction of a millimeter across, and the mineral proportions are inferred from that chemistry plus images, not measured directly in a lab. The source of the second water is unresolved: the authors write that the silica-depositing fluids were “likely supplied either by the Jezero paleolake itself or by groundwater” that had evolved through long contact with rock, and the rover data cannot tell those two apart. The heat behind the third episode is also an inference. The volcanic structure on the crater’s edge is a candidate, not a confirmed vent.

Timing is the largest gap. The sequence is relative: groundwater first, lake or evolved groundwater second, hot fluids last. The study does not put absolute ages on any of it, so it cannot say whether these episodes were separated by thousands of years or hundreds of millions. That answer needs laboratory dating of the cores themselves.

The samples are sealed, and still on Mars

Perseverance drilled two cores from the low-lying part of the Margin Unit, named Pelican Point and Lefroy Bay, plus a third, Comet Geyser, farther along the traverse. They were collected for a sample return mission that would carry them to Earth labs capable of dating them and searching them for microfossils.

That mission no longer has money behind it. Congress declined to fund the joint NASA and ESA Mars Sample Return campaign in its fiscal year 2026 appropriations, signed in January 2026. China’s Tianwen-3 mission aims to launch in 2028 and return its own Martian samples around 2031, from a different site.

The rover landed in Jezero in February 2021 and worked its way across the Margin Unit over roughly a year starting in September 2023. The study, published in Communications Earth & Environment on September 21, 2026, comes from that traverse. “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.

Common questions about the water history of Jezero Crater

Did Perseverance find water on Mars?

Not liquid water today. It found minerals that only form when water reacts with rock, showing that groundwater, a lake and later hot fluids all passed through the same volcanic rock in Jezero Crater billions of years ago.

What is the Margin Unit in Jezero Crater?

It is a band of olivine-rich rock along the inner edge of Jezero’s rim. Orbital data suggested it was an ancient lakeshore lined with carbonate. Perseverance showed it is igneous rock that water altered at least three times.

Why does carbonate on Mars matter for finding life?

On Earth, carbonate and silica minerals can preserve chemical and microscopic traces of microbes for billions of years. Rocks rich in both are among the best places to look for signs of ancient Martian life.

Will the Perseverance samples ever come back to Earth?

For now no mission is funded to collect them. The NASA and ESA sample return campaign lost its funding in 2026, and the cores remain sealed aboard the rover.

Reference: Bedford et al., “Lake- and groundwater-associated alteration of the olivine-rich Margin unit in Jezero crater, Mars,” Communications Earth & Environment, 2026. DOI: 10.1038/s43247-026-03997-9

Tags: astronomy, nasa, Mars, Jezero Crater, Mars exploration, Perseverance