This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When NASA's Perseverance rover reached the inner edge of Mars' Jezero Crater in September 2023, mission scientists were surprised by what they found. The geologic area, called the "Margin Unit," stretches along the shoreline of an ancient Martian lake, so they expected sedimentary rocks, which would have formed as layers of sand piled on top of each other over millennia.
Composed of clay and silt, sedimentary rocks 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 team found igneous rock, which can form deep underground from magma or 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. In this case, they preserved an astonishingly complex record of water activity on early Mars.
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. The findings were published Monday in the journal Communications Earth & Environment. The instrument behind the findings is SuperCam, which perches on the rover's mast and determines the mineralogy of geologic features based on the light they reflect.
When the science team spots an intriguing rock, it 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. Perseverance has analyzed more than 185 bedrock targets across the unit this way.
"Before we arrived at the Margin Unit, the main hypothesis—derived from orbital observations—was that the carbonate seen from orbit formed through interaction with the lake that existed in Jezero Crater," said Candice Bedford, a research scientist at Purdue University in West Lafayette, Indiana, and the study's lead author. "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." Perseverance explored the Margin Unit across approximately 870 feet (265 meters) of elevation.
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