Perseverance finds mineral-rich, 'polka-dotted' mudstones that may be signs of ancient Martian life

NASA’s Perseverance rover has collected a mudstone sample on Mars containing organic carbon and distinctive greenish "poppy seed" and "leopard spot" mineral textures that researchers say provide the most compelling in-situ evidence yet for past microbial activity on the Red Planet.

Researchers reported the findings Wednesday in a study published in Nature, describing clay-rich mudstones recovered from inside Neretva Vallis, an ancient river channel that once fed Jezero Crater. The rock contains carbon-bearing molecules and abundant nodules enriched in iron phosphate and iron sulfide—minerals that on Earth are produced when microbes metabolize organic matter, the authors said.

"The thing I find most exciting about this sample is that it contains features large enough to be seen with the naked eye that could be examined to test for past life," said Michael Tice, a member of the Mars 2020 science team, in remarks included with the study. Study lead author Joel Hurowitz of Stony Brook University described the discovery as "the first compelling signal of organic matter that we’ve had since we landed in Jezero Crater."

Perseverance has been exploring Jezero Crater and its inflowing channels since its landing in 2021 and has collected more than 30 samples; the newly reported specimen is the 25th analyzed with onboard instruments. The site where the sample was acquired—inside Neretva Vallis—represents a former fluvial environment where water transported and deposited fine sediments, conditions considered favorable for preserving organics.

The nodules are enriched in iron-bearing phosphates and sulfides. On Earth, such assemblages can form as by-products when microorganisms degrade organic material and react with surrounding sediments. Hurowitz called the nodules "a potential biosignature," but he and co-authors cautioned that nonbiological processes could produce similar features. Possible abiotic origins cited by the team include input from meteorites or mineral transformations driven by heat or chemical alteration.

"That’s part of the reason why we can’t go so far as to say, ‘A-ha, this is proof positive of life,’" Hurowitz said. The study notes the sample does not show evidence of heating that would be expected if thermal processes alone had produced the observed mineralogy, a factor the authors say strengthens the microbial interpretation but does not rule out other formation pathways.

Confirming a biological origin will require laboratory analyses on Earth, the researchers said. Edouard (Dauphas), a planetary scientist at the University of Chicago quoted in the study, said the rocks are "prime targets in the search for ancient life on Mars," and added that only a sample return could answer definitively whether life ever existed on Mars.

Plans for returning Martian samples to Earth were part of the original Mars Sample Return architecture tied to Perseverance. Those plans anticipated retrieval in the early 2030s, but program funding reductions have pushed that timeline back by roughly a decade, extending the expected return date into the 2040s, officials and the study note. Until then, the research team will continue to examine samples with Perseverance’s suite of instruments and compare the rover data with terrestrial laboratory experiments to test abiotic and biotic formation scenarios.

The new findings add to growing evidence that Jezero and its feeder channels preserved organic materials and complex chemical environments billions of years ago. The study emphasizes caution: while the mineral textures and molecular detections are consistent with a biological influence, they are not a conclusive demonstration of past life. Researchers say the most definitive test will come from targeted laboratory analyses of these rocks on Earth, should the samples be returned.