A recent analysis of the Sapphire Canyon mudstone core, drilled by NASA’s Perseverance rover in July 2024, provides intriguing new evidence in the ongoing quest for life on Mars. This groundbreaking study details the minerals and textures found in the core that, on Earth, are often associated with microbial activity. However, the authors caution that nonbiological chemistry could also account for these signals.
The core sample was extracted from a rock known as “Chevaya Falls”, located in Neretva Vallis, an ancient river channel approximately a quarter mile wide that once fed into the lake of Jezero Crater. After drilling, Perseverance sealed the sample for potential return to Earth, where laboratory instruments can conduct tests that exceed the capabilities of the rover's onboard tools.
Lead author Joel A. Hurowitz of Stony Brook University (SBU) describes the fine-grained mudstone exhibiting circular reaction fronts, informally termed as leopard spots, along with small nodules embedded in layered sediments. Utilizing Perseverance’s SHERLOC and PIXL instruments, the team mapped organic carbon alongside phosphate, iron, and sulfur arranged in distinct, repeating patterns. Notable minerals identified include vivianite and greigite.
Vivianite is an iron phosphate, while greigite is an iron sulfide associated with iron and sulfur cycling in oxygen-poor environments. These minerals are characteristic of rocks formed in water rather than from volcanic lava, suggesting that the Martian site is significant due to its geological history.
On Earth, vivianite typically forms in environments where microbes reduce iron in water-rich sediments, effectively trapping phosphorus in blue-green nodules. Laboratory and field studies have documented the biological processes that lead to the formation of vivianite through extracellular electron transfer mechanisms. Similarly, greigite is commonly associated with sulfate-reducing bacteria in anoxic muds. Controlled experiments have shown that greigite is detectable only in biotic conditions after extensive incubation.
The Martian rock exhibits rims rich in vivianite surrounding cores that are more abundant in greigite. This bullseye pattern aligns with a sequence of electron transfer reactions observed in certain Earth sediments. While this evidence doesn’t definitively prove that metabolism occurred in the Bright Angel mud, it does indicate that the chemistry is conducive to supporting life.
A potential biosignature refers to features that might indicate a biological origin but require further investigation to exclude nonbiological explanations. NASA encourages mission teams and the public to utilize the Confidence of Life Detection (CoLD) scale, which promotes a structured approach to claims about life. The CoLD framework involves first detecting a signal, then ruling out contamination, exploring alternatives, and only after thorough analysis discussing the possibility of life on Mars.
The Mars rover has detected organic carbon in several locations within Bright Angel. The reaction fronts lined with vivianite surround cores richer in greigite, which aligns with the iron and sulfur cycling recorded in the research. The mineral veins also include calcium sulfate, and the mudstone remains fine-grained, low in magnesium and manganese, without signs of intense heating that would disrupt its texture.
These observations indicate that the outcrop lies within layered sediments deposited by water flowing through Neretva Vallis. This ancient channel, spanning roughly a quarter mile, suggests a prolonged flow into Jezero’s ancient lake, creating a low-temperature environment that favors the chemistry necessary for life, although it does not confirm its existence.
“It’s not life itself,” emphasized Nicky Fox, associate administrator for NASA’s Science Mission Directorate, highlighting that this is merely a potential biosignature. Lead author Hurowitz echoed this sentiment, stating, “We cannot claim this is more than a potential biosignature.” Other officials reinforced the importance of being cautious in the interpretation of these findings, with acting NASA administrator Sean Duffy suggesting that this could be the clearest indication of life found on Mars to date.
If the vivianite and greigite were formed through microbe-like processes, then Bright Angel offers a glimpse into a period when surface waters could have supported chemical strategies similar to those some cells utilize for energy today. This would suggest that Mars’s habitability extended into a timeframe when this section of Jezero was still wet. Conversely, if abiotic processes created the same patterns, the rock still reflects the redox organization of iron, sulfur, and phosphorus in Martian mud, offering insights into how the planet cycles essential elements.
The authors propose lab experiments and field analogs on Earth to determine whether nonbiological reactions can replicate the observed textures and mineral pairings. They also indicate that further analyses requiring the sample in a clean Earth lab will be necessary, including isotope ratios that biological processes tend to skew. The ongoing planning for sample return will influence the speed at which these tests are conducted.
Meanwhile, the Perseverance rover continues to map the areas where these features are concentrated and how they relate to surrounding rock units. The capabilities of PIXL and SHERLOC have demonstrated sufficient sensitivity to guide this search, allowing for a consistent application of elemental mapping and Raman detections to other outcrops. As new targets are identified, the CoLD framework will aid in communicating progress without overstepping the data.
This meticulous approach is essential for transforming a potential biosignature into a reliable result that can be trusted by the scientific community.
The study has been published in the prestigious journal Nature.
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