NASA’s Perseverance rover has made a groundbreaking discovery of complex carbon compounds within a Martian crater, a site previously indicated as potentially harboring ancient life. On Earth, these compounds are often associated with biological remnants; however, scientists caution against jumping to conclusions, as such compounds can also emerge from non-living environments like meteorites.

In 2024, Perseverance explored a rocky outcrop named Bright Angel, located near what seems to be an ancient riverbed that once nourished a lake in Jezero Crater. Distinct mottling patterns observed on some rocks, dubbed “leopard spots” or “poppy seeds” by NASA scientists, comprise dark circular blotches measuring up to 1 millimeter in size. These patterns closely mimic those associated with ancient microbial activity on Earth.

While the possibility of abiotic origins remains, these signatures present some of the most compelling evidence for ancient life on Mars. However, comprehensive data regarding the chemical makeup and distribution of these patterns within the Bright Angel Formation was still lacking.

Equipped with advanced measurement tools, Perseverance is capable of providing crucial chemical insights about the rocks it examines, including the SHERLOC instrument. This tool uses ultraviolet laser reflections to identify elements and compounds present in rock samples.

According to Ashley Murphy, researchers at the Planetary Science Institute in Tucson, Arizona, utilized SHERLOC to detect large, complex carbon-containing molecules, known as polymeric carbon, on the surfaces of marked rocks within the Bright Angel Formation.

“On Earth, polymeric carbon is typically found in ancient rocks and can serve as a key indicator of past microbial life,” Murphy explains. “Identifying these organic macromolecules on Mars and other celestial bodies can enhance our understanding of the conditions that may once supported life.”

However, the finding of these carbon compounds does not automatically imply a biological origin, as they are also frequently discovered in meteorites, notes Lewis Dartnell from the University of Westminster, London. Murphy’s team also found that these compounds are linked to essential life-supporting minerals: carbonates and sulfates, which typically form in water-rich environments. “This context provides valuable insights into the geological environments where these organic materials exist,” Dartnell adds.

Jezero Crater is believed to have harbored abundant water at some point, making the presence of carbon compounds here consistent with expectations, according to team members like Kyle Uckert at NASA’s Jet Propulsion Laboratory in California. However, it is noteworthy that polymeric carbon has never been documented on the surfaces of such rocks before, raising questions about its resilience and distinctive nature compared to other carbon compounds found on Mars.

“Its widespread presence in the Bright Angel mudstone was unexpected in relation to other observations throughout the crater,” Uckert said. The reasons for this anomaly remain unclear, but Dartnell suggests that it may be an encouraging signal for discovering additional evidence of ancient life. “This detection confirms the potential for complex organic materials like these polymeric deposits to endure over geological timescales.”

While the SHERLOC tool can identify polymeric carbon, it cannot ascertain the precise composition of a compound beyond indicating it is carbon-rich, according to Sean McMahon from the University of Edinburgh, UK. “To determine if the carbon in these rocks is biologically derived, we would need to return samples to Earth,” he states.