Surface spots and nodules on rocks in ancient river valley are described in new study as ‘potential biosignatures’

 

Ian Sample Science editor and Richard Luscombe

Thu 11 Sep 2025 02.24 AEST

Unusual features found in rocks on Mars may be the handiwork of ancient microbial life that eked out an existence on the red planet billions of years ago.

The rocks were spotted by Nasa’s Perseverance rover as it trundled along Neretva Vallis, an ancient river valley that was carved into the landscape by water flowing into the Jezero crater in the planet’s distant past.

The rover, which touched down in Jezero crater in 2021, encountered the rocks last year as it explored an outcrop called the Bright Angel formation on the northern edge of the ancient valley.

“This very well could be the clearest sign of life that we’ve ever found on Mars,” Sean Duffy, Nasa’s acting administrator, told a press conference at the space agency’s Washington DC headquarters on Wednesday.

Instruments onboard the rover detected signs of carbon-based compounds in the rocks, while images captured intriguing surface spots and nodules that are often associated with microbial life on Earth.

The unusual features may have prosaic origins in the form of chemical reactions that played out over millennia. But in a report published in Nature on Wednesday, the findings of which were discussed at the press conference, scientists say the features should be regarded as potential signs of life.

“Our analysis leads us to conclude that the Bright Angel formation contains textures, chemical and mineral characteristics, and organic signatures that warrant consideration as ‘potential biosignatures’,” they write.

“It’s a signature. It’s a sort of leftover sign. It’s not life itself. And it certainly could have been from ancient life, and that would have been something that was there billions of years ago, nothing that’s currently there,” Dr Nicky Fox, associate administrator of Nasa’s science mission directorate, told reporters.

Still, she said: “We’re kind of one step closer to answering one of humanity’s most profound questions, and that is: are we truly alone in the universe?”

While Mars appears an arid world today, its surface is crossed and dotted with ancient river and lake beds, pointing to a warmer, wetter past. If life ever gained a foothold on the planet, traces may be found in its rocks as organic matter and possibly even fossilised organisms.

Dr Joel Hurowitz, a geochemist and planetary scientist at Stony Brook University in New York, and first author on the paper, said the unusual features on the rocks were accumulations of minerals, including an iron-phosphate mineral, vivianite, and an iron sulphide mineral, greigite.

“These minerals appear to have formed as a result of reactions between the mud of the Bright Angel formation and organic matter that is also present in that mud,” he said. The reactions appeared to have taken place shortly after the mud was deposited on the lake bed.

On Earth, reactions that combine organic matter and chemical compounds in mud to form new minerals, such as vivianite and greigite, are often driven by microbial activity. The microbes consume the organic compounds and produce the minerals as a byproduct of their metabolism.

But there are other ways to produce the minerals. “The reason … we cannot claim this is more than a potential biosignature is that there are chemical processes that can cause similar reactions in the absence of biology and we cannot rule those processes out completely on the basis of rover data alone,” Hurowitz said.

Hurowitz added: “We should be conservative and stick to the potential biosignature designation until future research and analysis on the sample collected from this geological formation can be performed on Earth.”

 

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The researchers hope the findings will kickstart efforts in laboratories to see if the intriguing features can be recreated through biological and non-biological processes. They also want it to spur fieldwork at sites where similar reactions may have taken place in the past. That would help scientists work out whether the features are biology at work.

Ultimately, confirmation may have to wait for Mars rocks, which have been stashed aboard Perseverance, to be brought back to Earth, but Nasa plans for such a mission are badly delayed and in doubt.

Scientists have decried what they see as “extinction-level cuts” to Nasa’s science budget by the Trump administration, including the likely axing of the Mars sample return mission that would allow such analysis.

Duffy, the transportation secretary installed by Trump at Nasa in July after withdrawing his initial nomination, refused to commit to bringing the rocks to Earth, and said it was the subject of “a current analysis”.

“We’re looking at how we get this sample back, or other samples back,” Duffy said. “We’re going to look at our timing. And, you know, how do we spend money better, and what technology do we have to get samples back more quickly?”

Fox appeared to press the case for more investment in Nasa’s scientific research in light of Wednesday’s announcement.

“Nasa science discoveries do not just happen at random. They are the rewarding results of meticulous, long-term strategic planning,” she said.

“We send these missions to really address these incredible questions, and each new discovery helps us drive what research is coming next.”

In an accompanying article to the report, Dr Janice Bishop, a planetary scientist at the Seti Institute in California and Dr Mario Parente, an expert in remote sensing on planets at the University of Massachusetts Amherst, said: “There is no evidence of microbes on Mars today, but if any had been present on ancient Mars, they too might have reduced sulfate minerals to form sulfides in such a lake at Jezero crater.”