NASA’s Perseverance rover discovered that the olivin-rich Margin Unit inside Jezero crater on Mars is not an ancient shoreline as scientists originally expected, but a volcanic rock altered by three distinct water systems over time. According to a study published on September 21, 2026, in Communications Earth & Environment, the site served as a hydrological intersection recording carbonated groundwater, a standing lake, and late hydrothermal fluid circulation.
SuperCam Laser Measurements Map 185 Rock Targets
The findings rest on data gathered by SuperCam, an instrument mounted on Perseverance’s mast approximately two meters above the surface. The device fires a laser at rock targets from up to 6.5 meters away, vaporizing a spot a few tenths of a millimeter wide to create a tiny plasma plume. An onboard spectrometer then reads the light emitted during cooling to identify elemental composition and mineral presence.
Perseverance targeted more than 185 rock outcrops across the Margin Unit while climbing roughly 265 meters in elevation along the crater wall. Lead author Candice Bedford, a researcher at Purdue University, and her colleagues sorted the results into chemical families and matched them with visual textures captured by a color camera. They then mapped each family against ancient water levels reconstructed from orbital terraces.
Three Sequential Water Environments Alter Volcanic Rock
The geological record reveals a sequence of fluid activity beginning deep underground. Neutral to alkaline groundwater rich in carbon dioxide moved through fractures in the bedrock, reacting with the green volcanic mineral olivine to deposit carbonate. “The cracks are like pipes, and the carbonate is Mars’ ‘calk’ that eventually plugged the ‘pipes,'” Bedford explained regarding the mineral veins.
A second, more acidic and cooler phase of water followed, dissolving some of the carbonate and filling small pores with silica. Co-author Eleni Ravanis from the University of Hawaiʻi at Mānoa and her team linked this stage to the Jezero paleolake itself or to long-term groundwater interaction. A third, hot phase subsequently drove late fluids through younger fractures, precipitating a 25-centimeter-thick vein of calcium sulfate and fluorite.
Margin Unit lacks organic molecules despite habitable chemistry
Jezero spans a 45-kilometer-wide crater that once held a river-fed lake, selected because orbital data detected carbonates along its rim. On Earth, carbonates and silicas excel at preserving chemical and microscopic signatures of ancient life.
The rock chemistry also points toward potential habitability, as water-olivine reactions on Earth can release hydrogen gas to sustain microbial life. However, the study reports no organic molecules or biosignatures within the Margin Unit. Methodological limitations remain, including the microscopic scale of SuperCam laser points and uncertainties regarding absolute timelines for the three fluid episodes.
Sealed Core Samples Await an Uncertain Return
Perseverance collected three core samples from the Margin Unit—named Pelican Point, Lefroy Bay, and Comet Geyser—and sealed them inside tubes on the rover. Those samples were gathered for a planned sample return campaign designed to bring them to terrestrial laboratories for absolute dating.
That mission currently lacks funding after Congress dropped financial support for the joint NASA and ESA Mars Sample Return campaign in appropriations signed in January 2026. Meanwhile, China’s Tianwen-3 mission aims for a 2028 launch to return separate samples around 2031. Researchers have not established absolute dates for the three-stage alteration sequence discovered in Jezero crater, leaving the exact time span between the groundwater, lake, and hydrothermal phases unknown.
Minerals reveal ancient water in Jezero crater
Did Perseverance find liquid water on Mars today?
No, the rover found mineral evidence showing that groundwater, a standing lake, and hydrothermal fluids passed through the same volcanic rock in Jezero crater billions of years ago.
What is the Margin Unit in Jezero crater?
It is a belt of olivin-rich magmatic rock along the interior of the crater rim that orbital data initially suggested was a carbonate-lined shoreline.
Why are carbonate rocks important for astrobiology?
On Earth, carbonate and silica minerals can lock in chemical and microscopic traces of ancient microbial life for billions of years.
Will the Perseverance core samples return to Earth?
No mission is currently funded to retrieve the sealed cores after the joint NASA and ESA return campaign lost its budget.
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