Nasa's Perseverance rover has detected complex carbon molecules in Martian rocks that are already under scrutiny for potential signatures of ancient microbial life. Measurements from the rover's Sherloc instrument identified organic carbon in mudstones from the Bright Angel outcrop, located along Neretva Vallis, a dried-up river that once carried water into Jezero crater billions of years ago.
The form of carbon detected, known as macromolecular carbon (MMC), can originate from living organisms but also from geological processes, so its presence does not confirm past life. Dr Ashley Murphy of the Planetary Science Institute noted that MMC may come from biological sources like fossilised organic matter or form through rock-water reactions or meteorite impacts.
The mudstones at Bright Angel caused excitement in 2024 when Perseverance found surface spots and nodules resembling features produced by fossilised microbes on Earth. Former acting Nasa head Sean Duffy described them as potentially the clearest sign of life yet found on Mars. The latest work, published in Science Advances, involved shining Sherloc's ultraviolet laser at the rocks and analysing the scattered light.
Tests on the Cheyava Falls mudstone revealed MMC on its surface, suggesting recent exposure or resistance to radiation and oxidation. This discovery means Nasa rovers have now found organic-bearing mudstones more than 2,000 miles apart on Mars, with Curiosity reporting similar finds in Gale crater. This indicates that habitability and organics may have been widespread billions of years ago.
Professor John Bridges of the University of Leicester called the work 'more tantalising information' about Bright Angel, noting that Jezero was a habitable environment with textures hinting at life and carbon building blocks. However, Perseverance's instruments cannot determine whether the carbon came from microbes or abiotic processes. Answers may come from returning samples to Earth, though Nasa's sample return mission was effectively cancelled in January; a revised mission is planned for the 2030s, while China aims to return samples in 2031.
