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A new study suggests a habitable past and signs of ancient microbial processes on Mars. Led by NASA and featuring key analysis from Imperial College London, the work has uncovered a range of minerals and organic matter in Martian rocks that point to an ancient history of habitable conditions and potential biological processes on the Red Planet.

An international team, including researchers from the Department of Earth Science and Engineering (ESE) at Imperial, propose that these geological features within the so-called Bright Angel formation in Mars's Jezero Crater are closely connected to organic carbon, and could be a compelling potential biosignature of past life.

Professor Sanjeev Gupta, Professor of Earth Science in ESE, and Academic Co-director of Imperial Global India, said, "This is a very exciting discovery of a potential biosignature but it does not mean we have discovered life on Mars. We now need to analyze this rock sample on Earth to truly confirm if biological processes were involved or not."

Promising signs

A core component of NASA's Mars 2020 mission, the Perseverance Rover has been exploring the 45-kilometer-wide Jezero Crater since 2021, a site chosen because it once held a huge lake and a river delta—environments that are considered prime targets in the search for signs of past life. Its key goal is to collect and store the first set of selected rock and soil samples that will be brought back to Earth for detailed analysis.

The new study, in Nature, focuses on a distinctly light-toned outcrop in the crater, dubbed "Bright Angel," located within an ancient river valley which provided water to the Jezero lake.

While driving through the valley, called Neretva Vallis, Perseverance came across a thick succession of fine-grained mudstones and muddy conglomerates. Here, it conducted a detailed analysis of these rocks, using instruments such as the Planetary Instrument for X-ray Lithochemistry (PIXL) and Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC).

An unexpected lake

By mapping the types and distributions of different sedimentary rocks at Bright Angel, ESE researchers (including Professor Gupta and Dr. Robert Barnes, a Research Associate in ESE) were able to reconstruct the environment in which these mudstones were deposited.

Their analysis revealed a range of sedimentary structures and textures indicative of lake margin and lake bed environments, including a composition rich in minerals like silica and clays—the opposite to a river scenario, where fast-moving water would carry these tiny particles away.

This pointed to a surprising conclusion: they had found lake deposits in the bottom of a river valley.

Co-author Alex Jones, a Ph.D. researcher in ESE and collaborating scientist with the NASA Perseverance team, who has conducted a detailed analysis of the ancient lake environment, said, "This is unusual but very intriguing, as we wouldn't expect to find such deposits in Neretva Vallis. What our sedimentological and stratigraphic work has done is indicate a past, low-energy lake environment—and that is precisely the kind of habitable environment we have been looking for on the mission."

The finding may suggest a period in the history of Jezero Crater where the valley itself was flooded, giving rise to this potentially habitable lake.

Jones, who is an Imperial President's Scholar and did his undergraduate degree in Earth and Planetary Science at ESE, added, "I'm thrilled to be involved in such a discovery and contributing to Perseverance operations during my Ph.D. It's also pretty cool to apply my terrestrial geologic field experience I gained as a student to investigate such an exciting unit at Jezero."

Compelling context

With the lake habitat scenario pinned down, the Perseverance science team turned their attention to the mudstones themselves. It was inside these rocks that they discovered a group of tiny nodules and reaction fronts, with chemical analysis revealing that these millimeter-scale structures are highly enriched in iron-phosphate and iron-sulfide minerals (likely vivianite and greigite).

These appear to have formed through redox reactions involving organic carbon, a process that could have been driven by either abiotic or—interestingly—biological chemistry. Importantly, this sets the stage for everything that happened next: the formation of this specific type of oxidized, iron- and phosphorus-rich sediment was the essential prerequisite for creating the ingredients for subsequent reactions.

Since these ingredients mirror by-products of microbial metabolism seen on Earth, it can be considered a compelling potential biosignature, raising the possibility that there was once microbial life on Mars.

A question for Earth labs

Ultimately, the only way for the true origin of these structures to be determined is by returning the samples to Earth, a possibility that rests on when future missions will manage to successfully collect the samples from Mars' surface.

Fortunately, Perseverance has already drilled and cached a core sample from the Bright Angel outcrop, named "Sapphire Canyon," which, along with others collected by the rover, is awaiting the Mars Sample Return mission—a joint NASA-ESA endeavor aiming to bring them to Earth in the 2030s.

Once in terrestrial laboratories, samples like Sapphire Canyon will be analyzed with instruments far more sensitive than those on the rover by scientists from around the world. Only then will we determine the precise origin of these features and whether they are the result of unique abiotic chemistry, or constitute evidence of past microbial life on Mars.

"This discovery is a huge step forward—the samples we helped characterize are among the most convincing we have," said Professor Gupta.

"The work was an impressive international effort and highlights the power of collaboration and advanced robotics in planetary exploration."

Matthew Cook, Head of Space Exploration at the UK Space Agency, said, "This exciting discovery represents a significant step forward in our understanding of Mars and the potential for ancient life beyond Earth. The chemical signatures identified in these Martian rocks are the first of their kind to potentially reflect biological processes that we see on Earth and provide more compelling evidence that Mars may have once harbored the conditions necessary for microbial life.

"Professor Sanjeev Gupta and his team at Imperial College London have made an invaluable contribution to this ground-breaking research, demonstrating the world-leading UK exploration science by leading the establishment of the geological context for the research.

"While we must remain scientifically cautious about definitive claims of ancient life, these findings represent the most promising evidence yet discovered. The upcoming Rosalind Franklin Mars rover mission, built here in the UK, will be crucial in helping us answer whether samples similar to those observed in this study represent genuine biological processes, bringing us closer to answering: are we alone in the universe?"