NASA's Perseverance rover has made a significant discovery on Mars, identifying complex carbon molecules in rocks that previously showed intriguing signs of ancient microbial life. The rover's Sherloc instrument detected what is known as macromolecular carbon (MMC) in mudstones from the Bright Angel outcrop, located within Neretva Vallis – a dried-up riverbed that once flowed into the Jezero crater billions of years ago.
While the presence of MMC is exciting, it does not conclusively prove the existence of past Martian life. Dr. Ashley Murphy of the Planetary Science Institute in Arizona, whose team published these findings, explained that MMC can derive from biological sources such as fossilised organic matter found in microbial mats or coal. However, it can also form through geological processes, such as reactions between rocks and water, or be delivered by impacting meteorites. This means further analysis is crucial to determine its origin.
The Bright Angel outcrop has been a focal point for scientists since 2024, when Perseverance first discovered surface spots and nodules that bore a striking resemblance to features created by fossilised microbes on Earth. At the time, Sean Duffy, former acting head of NASA, commented that these could be "the clearest sign of life that we’ve ever found on Mars." The latest detection of complex carbon, detailed in a study in Science Advances, was made by shining the rover’s ultraviolet laser onto these enigmatic rocks and analysing the scattered light.
A particularly interesting finding was the presence of MMC on the surface of one rock, the Cheyava Falls mudstone. This suggests either recent exposure to the Martian environment or a resilience to the harsh radiation and chemical oxidation that typically destroy organic materials on the planet's surface. This discovery also means that NASA rovers have now found organic-bearing mudstones over 2,000 miles apart on Mars, with similar reports from the Curiosity rover in the Gale crater. This widespread distribution "indicates that the habitability of Mars, and the availability of organics, may have been widespread across the planet billions of years ago," according to the study's authors.
Professor John Bridges, a planetary scientist at the University of Leicester, who was not involved in the research, noted that the work provides "more tantalising information" about the Jezero crater. He highlighted that the crater was clearly a habitable environment for primitive life, with both physical textures and the carbon building blocks suggesting the possibility of life in this ancient delta. However, current Mars rovers are not equipped to definitively distinguish between biological and non-biological origins of complex carbon. Dr. Kyle Uckert, a research scientist at NASA’s Jet Propulsion Lab and co-author, explained that the rover's payload was designed to identify compelling samples for return to Earth, where more rigorous testing can be performed. Professor Mark Sephton, an organic geochemist at Imperial College London, also a co-author, emphasised that these "treasure troves of information are puzzles that need to be solved," best achieved in Earth laboratories.
NASA had initially planned to bring Martian rock samples back to Earth sooner, but that mission was effectively cancelled in January. A revised mission is now being planned for the 2030s, with China also aiming to return its own Martian samples by 2031.
Source: Science Advances