- NASA's Perseverance rover found unexpected igneous rocks at Mars' Jezero Crater edge
- Scientists expected sedimentary rocks but discovered igneous rocks altered by water thrice
- SuperCam instrument analyzed over 185 rock targets using laser-induced plasma spectroscopy
NASA's Perseverance rover has found unexpected rocks at the inner edge of Mars' Jezero Crater. Scientists expected to find sedimentary rocks formed from layers of sand near an ancient lake. Instead, the rover discovered igneous rocks that showed signs of interacting with water at least three different times. The findings provide a complex record of water activity on early Mars. The study was published in the journal Communications Earth & Environment. When Perseverance reached the area in September 2023, scientists called it the "Margin Unit." The area stretches along the shoreline of an ancient Martian lake. Scientists expected sedimentary rocks because they can preserve signs of past microbial life. They were also interested in carbonate minerals detected by Mars orbiters because carbonates often form in shallow ocean and lake environments, according to NASA.
Instead, the rover found igneous rocks. These rocks can form deep underground from magma or through volcanic activity at the surface.
The mineral crystals inside igneous rocks can preserve details about when they formed. In the Margin Unit, they also showed that the rocks had interacted with water on at least three separate occasions.
The findings came from Perseverance's SuperCam instrument, which is placed on the rover's mast. It studies rocks by examining the light they reflect. When scientists find an interesting rock, SuperCam can fire a laser at it from up to 21 feet away. The resulting plasma shows the rock's chemical makeup. Perseverance has studied more than 185 bedrock targets across the Margin Unit using this method.
Study lead author Candice Bedford said scientists originally believed that the carbonate seen from orbit had formed through interaction with the ancient lake in Jezero Crater.
She said scientists now know that the location became a kind of crossroads for different water systems. She added that the findings are important because Jezero Crater is inside one of the largest areas of carbonate on Mars.
Perseverance explored the Margin Unit across about 870 feet of elevation. At higher elevations, it found coarse-grained, crystalline rocks containing olivine, with almost no signs of water.
The olivine formed deep underground from magma that cooled slowly. It later reached the surface after the ground above it was eroded away. Lower in the unit, near the lakebed, the rocks looked different. The olivine grains were fractured, with silica found between them.
Carbonate and silica are important in the search for ancient life. When water interacts with olivine on Earth, the reaction can release hydrogen, which can provide food for some microbes. The process also leaves carbonate and silica, which can preserve traces of past microbial life.
