NASA’s Perseverance rover discovered unexpected igneous rocks showing evidence of multiple water interactions along the inner edge of Mars’ Jezero Crater. The finding challenges long-held orbital theories about the region’s ancient lakebed environment and offers fresh clues regarding early Martian habitability.
When the Perseverance rover arrived at the inner shoreline of Mars’ Jezero Crater in September 2023, mission scientists anticipated a familiar geological landscape. The target zone, known as the “Margin Unit,” hugs an ancient Martian lakebed where researchers expected to find layered sedimentary rocks rich in clay and silt. Such deposits on Earth are good at preserving past microbial life. The scientists were especially intrigued by strong signals of carbonate minerals detected by Mars orbiters. On Earth, carbonates frequently form in shallow ocean and lake environments capable of supporting life.
Instead, the rover found igneous rock, which can form deep underground from magma or from volcanic activity at the surface. Igneous rocks are excellent record-keepers, particularly because mineral crystals within them preserve details about the precise moment they formed. Rather than a simple lakeshore, planetary scientists uncovered a complex, multi-stage water archive. In fact, these rocks showed signs of having interacted with water on at least three separate occasions, with each encounter further altering their chemistry and appearance.
SuperCam Laser Analysis Across 185 Bedrock Targets
To unravel the site’s geology, the science team utilized the SuperCam instrument mounted on the rover’s mast, which determines the mineralogy of geologic features based on the light they reflect. When the science team spots an intriguing rock, they can send commands for SuperCam to fire its laser up to 21 feet (6.5 meters) away. The spectrum of the resulting plasma reveals the target’s chemistry.
Throughout its traverse, Perseverance has analyzed more than 185 bedrock targets across the unit this way. At high elevations, the rock had the texture and chemistry of slow-cooled, olivine-rich rock without significant water exposure. Olivine is a mineral that formed as magma slowly cooled.
However, about 265 m (870 ft) lower, where the hypothesized ancient lake existed, there were signs indicating a complex history of rock-water interaction. In these lakebed areas, the rocks showed signs of physical and chemical alteration.
Three Distinct Episodes of Ancient Martian Water
By combining instrument data with spatial observations, researchers pieced together a sequence of at least three separate water-interaction events that reshaped the region, including one involving hot groundwater circulating beneath the ancient surface, according to a statement from the space agency. Mars may have been a much wetter and more geologically active world than it is today, with water repeatedly coursing through its rocks in different forms, a new study suggests.
During the first episode, carbon-dioxide-rich groundwater reacted with olivine. The findings were published Monday in the journal Communications Earth & Environment.
Reshaping Orbital Assumptions About Jezero Crater
The findings challenge long-standing interpretations built on orbital data. 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,
Candice Bedford, lead author of the study and a research scientist at Purdue University in West Lafayette, Indiana, said in the statement. “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.”
