NASA’s Perseverance rover has uncovered unexpected igneous rocks at the edge of Mars’ Jezero Crater, providing new evidence that water interacted with the planet’s rocks at least three separate times in the region.
The findings published in Communications Earth & Environment come from the rover’s exploration of an area known as the “Margin Unit,” which stretches along the shoreline of an ancient lake. Scientists had expected to encounter sedimentary rocks formed from material deposited by the lake.
Instead, Perseverance found igneous rocks, which form when molten rock cools and solidifies either underground or after volcanic activity at the surface.
The discovery is significant because the rocks preserve evidence of multiple episodes of interaction with water, offering scientists a more complicated picture of Mars’ ancient environment.
Perseverance reached the Margin Unit in September 2023. Scientists were particularly interested in the region because orbiting spacecraft had detected carbonate minerals there. Carbonates can form through interactions involving water and can sometimes preserve chemical or physical evidence associated with ancient environments.
Using its SuperCam instrument, Perseverance examined more than 185 bedrock targets across the Margin Unit. SuperCam can fire a laser at rocks from a distance of up to about 21 feet and analyse the resulting plasma to determine their chemical composition.
At higher elevations in the Margin Unit, the rover encountered coarse grained crystalline rocks containing olivine, with little evidence of alteration by water. Researchers concluded that the olivine originally formed deep underground as magma cooled slowly before geological erosion eventually exposed the rocks at the surface.
Further downhill, closer to the ancient lakebed, the rocks showed substantially more evidence of interaction with water. The olivine crystals were fractured, while silica was found between the grains.
Researchers say the different characteristics suggest that the area was influenced by multiple water systems rather than by a single period of lake activity.
Study lead author Candice Bedford said scientists had initially believed the carbonate minerals detected from orbit formed through interaction with the ancient lake. The new observations indicate that the geological history of the area was more complex.
The findings also have implications for the search for evidence of ancient microbial life. On Earth, water reacting with olivine can produce hydrogen which can serve as an energy source for certain microbes. Such reactions can also produce carbonate and silica, minerals that may preserve signs of past biological activity.
The discovery does not establish that life ever existed on Mars. Instead it provides scientists with new geological evidence about where water existed, how it interacted with rocks and which environments might have been capable of supporting microbial activity in Mars’ ancient past.
Jezero Crater remains a major target for Perseverance because its ancient lake and river environment could have preserved geological and potentially biological clues from a period when Mars was much wetter than it is today.