Redox-driven mineral and organic associations in Jezero Crater, Mars: A New Chapter in Astrobiology
NASA’s Perseverance rover has reached a significant milestone in the quest for signs of ancient life on Mars. A detailed geological, petrographic, and geochemical survey of distinctive mudstone and conglomerate outcrops in the Martian Jezero Crater’s Bright Angel formation has revealed intriguing characteristics that may point to potential biosignatures. This discovery is a monumental leap in astrobiology and planetary science.
The Perseverance rover, an integral part of Mars 2020 mission, has been on a mission to characterize early Martian geological processes and habitability and search for potential biosignatures within Jezero Crater. The Crater, once home to an ancient river delta, is believed to have conditions that could have supported microbial life billions of years ago.
Upon entering Neretva Vallis on the Crater’s western edge, Perseverance focused its attention on the Bright Angel formation, composed of distinctive mudstone and conglomerate outcrops. This formation was found to contain submillimetre-scale nodules and millimetre-scale reaction fronts enriched in ferrous iron phosphate and sulfide minerals, likely vivianite and greigite, respectively.
Interestingly, these mudstones in the Bright Angel formation were found to contain organic carbon. This organic carbon appears to have participated in post-depositional redox reactions that produced the observed iron-phosphate and iron-sulfide minerals. Given the geological context and petrography, these reactions are believed to have occurred at low temperatures, adding a new dimension to our understanding of Mars’ geological history.
Such redox reactions that involve organic matter can produce a suite of iron-, sulfur-, and phosphorus-bearing minerals. This is evident in both laboratory simulations and natural environments on Earth. The analysis of the core sample collected from this unit, when enabled through high-sensitivity instrumentation, could help determine the origin of the minerals, organics, and textures it contains.
An intriguing find during the rover’s exploration was the leopard spots on a rock sample. Many scientists believe these spots may have potentially been made by ancient life. Nicknamed “Cheyava Falls,” this reddish rock was discovered in July 2024 in Mars’ Jezero Crater. This sample, safely tucked away in a tube millions of miles away on Mars, could reveal whether microscopic life ever existed on the red planet.
The Perseverance rover collected the sample, called Sapphire Canyon, from rocky outcrops on the edges of the Neretva Vallis river valley. This region was sculpted by water that once flowed into Jezero Crater more than 3 billion years ago. The discovery of a potential biosignature on this rock, which could be consistent with biological processes, marks a significant step in the Mars 2020 mission.
Cheyava Falls showcased small black spots, nicknamed “poppy seeds” by Perseverance’s science team, and larger markings dubbed leopard spots. The rover’s Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) instrument detected organic compounds in the rock, indicating that ancient chemical reactions within the rock once supported microbial organisms.
The white veins of calcium sulfate present clear evidence that water — crucial for life — once ran through the rock. The irregular-shaped leopard spots detected iron and phosphate within the features, which may have occurred when chemical reactions with hematite turned the rock from red to white. These reactions can provide an energy source for microbes, further supporting the possibility of ancient life on Mars.
Since landing on Mars, Perseverance has been collecting samples that were intended to be returned to Earth by future missions. As we wait for the return of these samples, these intriguing finds by the rover continue to fuel our curiosity and fascination about life beyond Earth.