NASA’s Perseverance rover has detected complex organic carbon molecules in Martian mudstone rocks within an ancient riverbed, delivering the most robust organic detection yet in Jezero Crater and adding significant weight to the possibility that microbial life once existed on the Red Planet.
The findings, published June 24 in the journal Science Advances, confirm the presence of macromolecular carbon (MMC) in two mudstone samples from the Bright Angel outcrop, a rocky formation within Neretva Vallis. This ancient river channel, stretching roughly 400 meters (1,300 feet) wide, once carried water into the vast lake that filled Jezero Crater billions of years ago.
“Measurements of two mudstones show hundreds of organic detections, making this the most robust organic detection in Jezero crater thus far, and, to our knowledge, the only detection of macromolecular carbon on a natural rock surface on Mars,” the research team wrote in their paper.
The discovery was made using SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals), a spectrometer mounted on the end of Perseverance’s 2-meter (7-foot) robotic arm. SHERLOC fires ultraviolet lasers at rock surfaces to identify mineral and organic compounds through Raman spectroscopy, a non-destructive technique that reveals molecular composition.
Carbon where it should not survive
What makes the finding particularly striking is where the carbon was found. The organic molecules were detected just a few microns beneath the Martian surface, thinner than a sheet of paper. On Mars, intense solar radiation and powerful oxidizing chemicals rapidly break down complex organic molecules, making their preservation at such shallow depth a remarkable surprise.
“The Martian surface environment includes radiation and chemical oxidants that are destructive to organics,” said Ashley Murphy, a researcher at the Planetary Science Institute and co-lead author of the study. “The MMC detected in the Bright Angel mudstones is either resistant to degradation and/or has been sufficiently shielded by other minerals, such as clays, or iron-rich Martian soil.”
The research team analyzed two distinct mudstones and found that the organic carbon was associated with different minerals in each. In one rock, the carbon was mixed primarily with silicate-dominated sediment. In the other, it appeared alongside secondary carbonate and sulfate minerals that formed later through aqueous alteration. This dual association suggests that organic compounds were deposited during at least two separate geological episodes: first when the sediments originally settled, and later when fluids moved through and chemically altered the rock.
Connection to the “leopard spots”
The carbon-bearing mudstones sit in the same location where Perseverance made headlines last year with the discovery of a rock nicknamed Cheyava Falls. That arrowhead-shaped rock, measuring 1 meter by 0.6 meters (3.2 feet by 2 feet), features distinctive millimeter-sized “leopard spots” surrounded by dark halos. These spots carry the signature of two iron-rich minerals: vivianite (hydrated iron phosphate) and greigite (iron sulfide).
On Earth, vivianite is frequently found in sediments, peat bogs, and around decaying organic matter, while certain forms of microbial life can produce greigite. The combination of these minerals, which appear to have formed by electron-transfer reactions between sediment and organic matter, represents a potential fingerprint for microbial life that would use these reactions to produce energy.
Scientists caution that the minerals also can form abiotically, or without the presence of life, through sustained high temperatures, acidic conditions, or binding by organic compounds. However, the Bright Angel rocks do not show evidence of high temperatures or acidic conditions, and researchers remain uncertain whether non-biological processes alone could have produced the observed patterns.
A wider distribution of organics on Mars
The detection carries implications far beyond Jezero Crater. NASA’s Curiosity rover previously detected organic compounds in sedimentary rocks at Gale Crater, more than 3,500 kilometers (2,200 miles) away. The new finding at Bright Angel marks the first time macromolecular carbon has been confirmed in a mudstone outside Gale Crater, suggesting that organic compounds were far more widespread across ancient Mars than previously believed.
“This is also the first detection of MMC in a mudstone on Mars outside of Gale Crater, suggesting that the availability of organics may have been widespread across the planet billions of years ago,” said Kyle Uckert, SHERLOC deputy principal investigator at NASA’s Jet Propulsion Laboratory and co-lead author of the study.
“It is encouraging for Martian habitability,” Murphy added. “This indicates that billions of years ago, organics may have been more than just locally present and may have been more widely available in ancient lakes and rivers on Mars.”
Life or geology? The answer awaits Earth labs
Despite the excitement, the Perseverance rover cannot determine whether the organic carbon was produced by ancient microbial life or by purely geological processes. The rover’s science payload was designed not to distinguish between biotic and abiotic origins, but rather to identify compelling rocks for collection and possible return to Earth.
“The science payload of the Perseverance rover was not designed to distinguish between abiotic and biotic processes, but was instead selected to identify compelling rocks to be collected for possible return to Earth for more rigorous testing,” Uckert said.
Multiple non-biological explanations remain viable. The carbon could have been delivered to the Martian surface by meteoritic infall, formed through hydrothermal geologic reactions, or generated by atmospheric processes. Determining the true origin will require laboratory analysis on Earth using far more sensitive instruments than any rover can carry.
Perseverance has already cached 30 rock and regolith samples, including a core named Sapphire Canyon taken from the Cheyava Falls rock that contains this organic carbon. These samples await a future Mars Sample Return mission, though budget uncertainties and shifting priorities at NASA have complicated the timeline for bringing them to Earth.
“If laboratory analyses reveal that the molecules formed abiotically, that would enhance scientists’ understanding of how complex organic chemistry can function sans life,” said Paul Byrne, a planetary scientist at Washington University in St. Louis. “Or perhaps we will find that these compounds were produced by alien biology. That possibility is worth bringing these samples back to Earth.”
For now, the Cheyava Falls rock is on the first rung of NASA’s seven-step Confidence of Life Detection (CoLD) scale, classified as a “possible signal.” Each additional piece of evidence, including the new organic carbon confirmation, helps build the case for what would be one of the most profound discoveries in scientific history: that life once existed beyond Earth.
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