View larger/ full image. | Partial view of the Margin Unit in Jezero crater on Mars. The Perseverance rover has found evidence for complex, long-gone water systems in this location. Image via NASA/ JPL-Caltech/ MSSS.

• Mars was once a much wetter planet than it is today, with plenty of liquid water on its surface.
• Mars’ water systems were more complex than previously known, according to new findings from the Perseverance rover.
• Rocks along the former lakeshore of Jezero crater interacted with water in three major episodes, the new findings show, including hot hydrothermal water.

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Water systems on early Mars

Mars is a dry planet now, but it was once awash in water. That includes Jezero crater, where the Perseverance rover is still exploring. Perseverance has already found ample evidence that the crater used to be a lake with rivers emptying into it. And now, scientists have found that the water system in Jezero crater was even more complex than previously thought.

Led by Purdue University in Indiana, the researchers said on September 21, 2026, that a region in the crater called the Margin Unit was shaped by a complex sequence of ancient lakes, groundwater systems and hydrothermal fluids.

The Margin Unit is along the shoreline of the ancient lake. The rover explored across about 870 feet (265 meters) of elevation on the Margin Unit.

The new peer-reviewed findings were published in Communications Earth & Environment on September 21, 2026.

An unexpected discovery

Before Perseverance landed in Jezero crater, scientists had expected to find sedimentary rocks at the landing site. These rocks would be composed of sand, clay and silt. They are great at preserving traces of ancient microbial life. But the researchers were in for a surprise. The rocks were not sedimentary, but igneous, which form from volcanic activity.

Igneous rocks can preserve details about minerals, how they formed and interactions with water. And it’s in these rocks that Perseverance found the clues to a complex water system in the past. The rover used its SuperCam instrument to analyze the rocks and determine their composition.

Jezero crater used to be a lake billions of years ago. Image via NASA/ JPL-Caltech.3 separate water episodes

Orbiting spacecraft have detected minerals known as carbonates in Jezero crater. And these carbonates are a key to this new discovery. As lead author Candice Bedford at Purdue University explained:

Before we arrived at the Margin Unit, the main hypothesis — derived from orbital observations — was that the carbonate seen from orbit 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. The Margin Unit findings are important because Jezero crater sits inside one of the largest exposures of carbonate on Mars, so what we learn here reaches well beyond this crater.

The rover has found that the rocks interacted with water on three primary occasions.

In the first episode of water interaction, carbon-dioxide-rich groundwater reacted with olivine. This formed ridges of carbonate that run through the fractures in bedrock at low elevations. Those ridges are still there today.

The second episode involved water from the former lake. Co-author Eleni Ravanis, a planetary scientist at the University of Hawaii at Manoa, said:

Some of the Margin Unit rocks also contain silica. Turning olivine into carbonate can leave silica behind, and we see more of that silica in rocks that sat below the water line.

Early water systems on Mars included hydrothermal activity

The final water episode created mineral veins at one location in the eastern part of the Margin Unit. They are about 10 inches (25 centimeters) thick and contain minerals like calcium sulfate and fluorite. This finding is particularly interesting, since it indicates that hydrothermal fluids — hot water — once flowed through the rocks.

As is almost always the case, there are surprises waiting when you are exploring another world. As Bedford summarized it:

If there is one thing I have learned after 10 years working with Mars rovers, it is that Mars constantly throws surprises at you. It is very rare that things are as we expect them to be from orbital data. I hope this work helps reshape how scientists view the history of water in Jezero crater and across Mars. Ultimately, I hope it helps planetary scientists reconstruct the changing climate and habitability of early Mars.

Candice Bedford, a research scientist at Purdue University, led the new study about water systems on Mars. Image via Purdue University.Subsurface olivine

Another notable discovery was that of olivine. At higher elevations in the Margin Unit, the rocks were course-grained and crystalline. That’s evidence for the mineral olivine. Plus, it was untouched by water. Instead, the olivine formed in a body of hot magma underground. It then gradually cooled. It was exposed on the surface when the ground above it eroded away.

Lower down in the Margin Unit, the olivine grains have silica between them. And interestingly, the carbonate and silica are important clues to possible past microbial life. On Earth, when water interacts with olivine, the reaction can release hydrogen, which can be a food source for some microbes. And it leaves behind carbonate and silica, two minerals that can preserve traces of the ancient microbes.

Last year, researchers in France also reported finding evidence for ancient hydrothermal systems in Jezero crater.

Bottom line: NASA’s Perseverance rover has found evidence of ancient complex water systems on early Mars, including hot hydrothermal activity.

Source: Lake- and groundwater-associated alteration of the olivine-rich Margin unit in Jezero crater, Mars

Via NASA

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