A study published on September 21, 2026, reports that rocks in the Margin unit of Mars’s Jezero crater preserve at least three relative episodes of ancient water-rock alteration. Perseverance examined the formation with its SuperCam instrument, finding a sequence that runs from carbon-dioxide-rich fluids and carbonate deposits to silica and a later vein that may record hydrothermal activity.
The result expands the story of Jezero’s past water. It also gives scientists a particularly interesting set of rocks for studying ancient habitability: carbonates and silica can preserve chemical clues about former environments, while some water-rock reactions can produce energy sources relevant to microorganisms. The study concerns ancient geology, not a detection of life or present-day liquid water.
Perseverance found a more complex history in Jezero
Perseverance began exploring the Margin unit in September 2023, after NASA’s rover landed in Jezero crater in February 2021. The formation lies along the crater’s inner edge, an area previously considered a possible ancient lakeshore.
SuperCam analyzed more than 185 bedrock targets across the unit. The higher exposures, above approximately −2,350 meters, are crystalline, olivine-rich igneous rocks with little apparent alteration by water. Lower exposures contain fractured olivine, carbonate-related features, silica, and other signs of interaction between fluids and rock.
Olivine is a common magnesium- and iron-rich mineral in igneous rocks. When fluids react with it, they can transform the original mineral and leave behind a new chemical record. That record is what allowed the study to separate the unit’s original rock from changes produced later by water.
Three relative episodes are recorded in the minerals
The stages do not have precise calendar dates. They are arranged in relative order, with each episode representing a different period of fluid activity.
| Relative episode | Fluid or process | Mineral record | What it indicates |
| First | Neutral-to-alkaline fluids rich in carbon dioxide circulated through fractures | Carbonate-rich fracture fills and ridges | An early period of water-rock alteration in the bedrock |
| Second | Lake water or evolving groundwater remobilized carbonate and moved through pore spaces | Silica precipitated in secondary pore spaces | A later phase involving lake-related or groundwater alteration |
| Third | Younger fractures were filled by late-stage fluids | Fluorite-bearing calcium-sulfate veins | A possible late hydrothermal phase; that origin is a likely interpretation, not a definitive result |
Carbonate is especially useful because it can preserve chemical information about the fluids and environments that formed it. Silica can also survive geological alteration and retain clues about how those fluids moved through the rock.
One striking feature is the Point Cloates vein. It is approximately 25 centimeters thick and extends several meters toward the east and northeast. Its fluorite-bearing calcium-sulfate composition fits the study’s interpretation of a late fluid event. The proposed hydrothermal origin remains a possibility rather than a settled mechanism.
Why this matters for the search for ancient life
The Margin unit is valuable for astrobiology because it contains several kinds of mineral evidence in one geological setting. Carbonates and silica may preserve chemical traces of ancient environments. In addition, reactions between water and olivine can potentially produce hydrogen, a chemical energy source used by some microorganisms on Earth.
That makes the rocks relevant to questions about habitability—the conditions that could support life—or preserve a biosignature. It does not turn those conditions into evidence that life existed on Mars. The study reports water-rock alteration and environments of astrobiological interest, not a life discovery.
The same distinction applies to Mars’s water today. The study reconstructs ancient interactions involving lake water, groundwater, and possibly later hydrothermal fluids; it does not report present-day liquid water.
What the samples could reveal on Earth
Perseverance collected the Pelican Point and Lefroy Bay samples from the Margin unit for potential future return to Earth. If a future mission brings them back, laboratories on Earth could examine their minerals and chemistry with instruments more powerful and flexible than those carried by a rover.
Those samples could help distinguish the roles of lake water and groundwater in the silica-bearing rocks, refine the sequence of alteration, and test the interpretation of the Point Cloates vein. No sample-return date or returned-sample result is established.
For now, Jezero’s Margin unit offers something almost as valuable as a simple answer about whether Mars once had water: a layered geological record showing that the planet’s ancient fluids acted more than once, and not always in the same way.
