After decades of robotic exploration of Mars, NASA has found the strongest evidence to date that the red planet once hosted life. This comes from rocks discovered by the robotic vehicle Perseverance, whose analysis suggests they could have formed through microbial chemical processes, potentially involving living organisms. The finding, made in the Jezero crater, was cautiously announced in a study published in the journal Nature and in a NASA press conference.
As acting NASA director Sean Duffy explained, after a year of studying the sample, they have not found another explanation: "This could be the clearest sign of life we have ever found on Mars, which is incredibly exciting." The identification of a possible biosignature is, for the agency's top official, "a revolutionary discovery that will expand our understanding of Mars."
Biosignatures are chemical traces of processes that may have involved the presence of life in the past or present, and are one of the tools that astrophysicists use to search for evidence of life beyond Earth. As NASA detailed in a statement, "a possible biosignature or potential biosignature is a substance or structure that could have a biological origin, but requires more data or additional studies before reaching a conclusion about the absence or presence of life."
Also, Nicola Fox, NASA's associate director for scientific missions, considers it "the closest they have been to finding life on Mars," but clarified that they have not found "evidence of life itself." The NASA chief scientist explained what they observed in this sample: "They are like fossil remains, remnants of a meal, and perhaps that meal was excreted by a microbe."
Since February 2021, the Perseverance rover has been exploring the Jezero crater in search of signs of ancient Martian life, as scientists know that billions of years ago, the planet had bodies of water and a climate suitable for hosting life. In fact, they believe it was quite similar to Earth during that period until it became the extreme desert it has been for the last 2.8 billion years.
In this search for clues of past life, NASA's vehicle collected this sample a year ago in the Bright Angel formation of an ancient valley called Neretva Vallis. 3.8 billion years ago, a river flowed through this area into a lake located in the current Jezero crater, depositing its sediments. Specifically, the scientific instruments of Perseverance discovered that these sedimentary rocks from the Bright Angel formation are composed of clay and silt, which on Earth are excellent preservers of past microbial life. They are also rich in organic carbon, sulfur, oxidized iron (oxide), and phosphorus, as detailed by NASA.
"The combination of chemical compounds found in the Bright Angel formation could have been a rich source of energy for microbial metabolism," declared Joel Hurowitz, the researcher from Stony Brook University who led the analysis published in Nature, and in which Spanish researchers from the Center for Astrobiology (CAB/CSIC-INTA), the University of Valladolid (UVA), and the Institute of Geosciences of the CSIC also participated.
Felipe Gómez, from the Center for Astrobiology, is a member of the Martian rovers missions Curiosity and Perseverance and one of the Spaniards who studied this sample: "On Earth, these types of reactions occur due to the action of extremophile microorganisms. We believe that the finding is highly relevant, but we cannot say that it is directly related to life because we have not seen any fossils of any microorganism," he explained in a phone conversation.
The sample collected by NASA's robotic vehicle and analyzed by this team has been named Shappire Canyon and contains tiny nodules of clay minerals enriched with iron phosphate and iron sulfide. These are compounds associated with organic carbon, meaning they could have formed in chemical reactions that are the basis of life, according to the scientists. Additionally, the team has confirmed that these processes occurred after the sediments were deposited in the lake and under low-temperature conditions, which, according to Felipe Gómez, is another element that makes this rock sample a possible biosignature.
However, the authors emphasize caution and warn that the same clues pointing to these rocks possibly being formed by microbes billions of years ago could also be the result of abiotic (non-biological) geological processes.
"Astrobiological claims, particularly those related to the possible discovery of past extraterrestrial life, require extraordinary evidence," stated Katie Stack Morgan, a scientist on the Perseverance project at NASA's Jet Propulsion Laboratory. "The publication of such a significant finding as a possible biosignature on Mars, peer-reviewed, is a crucial step in the scientific process, ensuring the rigor, validity, and relevance of our results. And although, considering the findings of the article, the abiotic explanations of what we observe are less likely, we cannot rule them out."
In that regard, her colleague Nicola Fox, NASA's associate director for scientific missions, also emphasized that they are making this data available to the entire scientific community for additional studies to confirm or refute its biological potential.
According to Felipe Gómez, Perseverance has already conducted all the analyses its instruments allow, and the only way to confirm that this sample contains evidence of past microbial life would be to bring it to Earth for detailed study.
"Definitive tests can only be carried out on the core sample of Sapphire Canyon if it is brought to Earth for study," Hurowitz agreed.
Mission to bring the samples to Earth in jeopardy
The robotic space mission designed to bring the samples collected by the rover back to Earth, called Mars Sample Return, was already planned, but its implementation is seriously threatened by the significant budget cuts proposed by the Donald Trump Administration for NASA's science department.
If this controversial funding cut for NASA's scientific missions materializes - Congress will have the final say - the ambitious robotic mission to retrieve the samples would be one of those canceled.
In this regard, Sean Duffy stated that NASA is exploring other possible ways to bring the samples back or even considering sending equipment to Mars for additional analysis. "We will review our budgets and timelines, how to best invest the money, and what technology we have to retrieve the samples more quickly," said the acting NASA director, who assures that "the president [Trump] loves space."