NASA’s Perseverance Rover Finds Evidence of Three Water Events on Ancient Mars

When NASA’s Perseverance rover reached the inner rim of Mars’ Jezero Crater in September 2023, mission scientists were surprised by what they found. The geological region, known as the Margin Unit, stretches along the shoreline of an ancient Martian lake. Scientists expected it to contain sedimentary rocks formed from layers of sand and silt over thousands of years.

Sedimentary rocks on Earth are often excellent at preserving evidence of past microbial life. Scientists were especially intrigued by the strong signal of carbonate minerals in the region. On Earth, carbonates frequently form in shallow ocean and lake environments that can support life.

Instead, Perseverance discovered igneous rock. These rocks can form from magma deep underground or from volcanic activity at the surface. They are also valuable geological record-keepers because their mineral crystals preserve details about the conditions in which they formed.

In the Margin Unit, the rocks preserved a surprisingly complex record of water activity on early Mars. The evidence shows that water interacted with the rocks at least three times, changing their chemistry and appearance each time. The findings were published in Communications Earth & Environment.

Perseverance’s SuperCam reveals the rocks’ chemistry

The instrument behind the discovery is SuperCam, which sits on Perseverance’s mast and determines the mineralogy of rocks by analyzing the light reflected from them. When scientists identify an interesting target, they can command SuperCam to fire a laser at a rock up to 21 feet (6.5 meters) away.

The spectrum produced by the resulting plasma reveals the target’s chemical composition. Perseverance has analyzed more than 185 rock targets using this method.

“Until we arrived at the Margin Unit, the main hypothesis derived from orbital observations was that the carbonates seen from orbit formed through interaction with the lakes present in Jezero Crater,” said Candice Bedford, a research scientist at Purdue University in West Lafayette, Indiana, and lead author of the study.

“But we now know that this site was a kind of crossroads for water systems. The discovery of the Margin Unit is important because Jezero Crater lies within one of the most exposed carbonate regions on Mars, so what we learn here extends far beyond the crater.”

Ancient Martian rocks record changing water conditions

Perseverance explored the Margin Unit across an elevation difference of approximately 870 feet (265 meters). At higher elevations, the rover found coarse-grained, crystalline rocks rich in olivine, with little evidence of contact with water.

These olivine-rich rocks contain magnesium and iron. They formed from a large mass of magma deep underground and reached the surface only after the crystals cooled slowly enough to grow large and the overlying ground eroded away.

In the lower part of the unit, on the ancient lakebed, the rock appears deformed. Olivine particles were crushed together with silica between them, creating a different appearance from the less altered rocks at higher elevations.

Carbonate and silica minerals are important clues in the search for ancient life. When water interacts with olivine on Earth, the reaction releases hydrogen, which can serve as an energy source for some microbes. The process also leaves behind carbonate and silica, minerals that can preserve traces of past microbial activity.

Three water-related events shaped Jezero Crater’s Margin Unit

Perseverance’s science team can determine the sequence of water-related interactions that affected the Margin Unit, although the rover cannot determine exactly when they occurred.

During the first event, carbon dioxide-rich groundwater reacted with olivine. This process formed carbonate ridges that filled cracks in the rock at lower elevations. Today, the carbonate-filled fractures remain in place as the surrounding, softer rock continues to wear away.

The second water interaction may have been connected to a lake that once occupied Jezero Crater.

“Some of the rocks in the Margin Unit also contain silica,” said Eleni Lavanis, a planetary scientist at the University of Hawaii at Manoa and co-author of the study. “Converting olivine to carbonate can leave behind silica, which is often found in rocks below the waterline.”

The final identified water event produced a vein approximately 10 inches (25 centimeters) thick. It also created minerals including calcium sulfate and fluorite in one location in the eastern portion of the Margin Unit.

Fluorite typically forms when hot water circulates through volcanic rocks. Its presence provides important evidence that the area later experienced a heated groundwater event.

“If there’s one thing I’ve learned from working with Mars rovers for 10 years, it’s that Mars always throws surprises at you,” Bedford said. “It’s very rare that things turn out exactly as we expect from orbital data. We hope this work will help scientists reconstruct how they view the history of water in Jezero Crater and across Mars. Ultimately, we hope it will help planetary scientists reconstruct the changing climate and habitability of early Mars.”

Perseverance continues the search for ancient life on Mars

The primary objective of Perseverance’s mission is astrobiology, including the search for signs of ancient microbial life. The rover is characterizing Mars’ geology and past climate while collecting and storing Martian rocks and regolith for further study.

NASA’s Jet Propulsion Laboratory in Southern California, managed by the California Institute of Technology, oversees the construction and operation of the Perseverance spacecraft on behalf of NASA’s Science Mission Directorate. The rover is part of NASA’s Mars Exploration Program portfolio.

SuperCam is jointly led by Purdue University in Indiana, Los Alamos National Laboratory in New Mexico, IRAP (Institute of Astrophysics and Planetology), and CNES (National Center for Spatial Research) in Toulouse, France.

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