A study published in Nature has presented the most persuasive evidence so far that ancient life may have once existed on Mars. The findings, based on observations from NASA’s Perseverance rover, will need to be confirmed through detailed examination of collected rock samples once they are returned to Earth.
The research team, which included professor Joel Horowitz of Stony Brook University, identified microscopic traces of organic compounds in a Martian rock. This discovery has led scientists to suggest that biological activity could have occurred on the planet in the distant past.
Astrobiologist Sean McMahon of the University of Edinburgh described the results as the strongest evidence yet for extraterrestrial life, calling it potentially one of the most significant scientific milestones in history.
The strongest evidence yet to ancient life on Mars
In mid-2024, Perseverance studied a clay-rich rock known as Cheyava Falls, which was shaped by liquid water roughly 4 billion years ago. Unlike most Martian rocks that display only a thin surface layer of oxidized iron, Cheyava Falls is red throughout.
The rock’s surface is dotted with pale spots, each smaller than a millimeter, encircled by a dark, phosphorus-rich mineral. Within these spots, researchers detected organic compounds — the same fundamental chemical building blocks of life found on Earth.
Scientists believe these markings are linked to redox, or oxidation-reduction, reactions in which electrons may have been transferred from organic matter. On Earth, comparable “reduction spots” appear in rocks and sediments where microbial activity consumed organic materials. The study further confirmed that the Martian spots contained organic matter along with an iron sulfide mineral, a combination often associated with microbial processes.
Awaiting Earth-based analysis
Despite the strength of the findings, researchers emphasize that a non-biological explanation cannot yet be ruled out. McMahon noted that in astrobiology, the absence of a convincing non-biological explanation often marks the true beginning of the search for life. He added that many major scientific breakthroughs in the past emerged only after alternative explanations had been eliminated.
To reach a definitive conclusion, the rock samples collected by Perseverance must be transported back to Earth. This effort is planned as part of the Mars Sample Return mission, a joint project of NASA and the European Space Agency. The initiative faces considerable challenges, particularly its high cost, which could reach tens of billions of dollars.
Still, McMahon stressed the potential payoff. If confirmed, he said, the discovery of ancient life on Mars could rank as the most important scientific revelation in human history.