Nasa's Perseverance rover has detected complex carbon molecules in Martian rocks that are already under scrutiny for potential signs of ancient microbial life. The discovery was made using the rover's Sherloc instrument, which identified organic carbon in mudstones from the Bright Angel outcrop in Neretva Vallis, a dried-up river that once flowed 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. Dr Ashley Murphy of the Planetary Science Institute in Arizona noted that MMC may come from biological sources such as fossilised organic matter, or form through rock-water reactions or meteorite impacts. This ambiguity means the detection does not confirm past life.
The Bright Angel mudstones previously caused excitement in 2024 when Perseverance found surface spots and nodules resembling features produced by fossilised microbes on Earth. Sean Duffy, former acting head of Nasa, described them as potentially the clearest sign of life ever found on Mars. The latest analysis, published in Science Advances, reveals MMC on the Cheyava Falls mudstone, suggesting recent exposure or resistance to radiation.
This discovery means Nasa rovers have now found organic-bearing mudstones more than 2,000 miles apart on Mars, with the Curiosity rover reporting similar finds in Gale crater. The authors state this indicates that habitability and organic availability may have been widespread billions of years ago. Professor John Bridges of the University of Leicester called the findings tantalising, noting that Jezero was a habitable environment with carbon building blocks.
However, the rovers cannot determine whether the carbon came from ancient microbes or non-biological processes. Dr Kyle Uckert of Nasa's Jet Propulsion Lab emphasised that the best way to resolve this is to return samples to Earth for rigorous testing. Nasa's sample return mission was effectively cancelled in January, but a revised mission is planned for the 2030s, while China aims to return samples in 2031.
