The scientific community has eagerly awaited news that could fundamentally change our understanding of the Red Planet. After more than a year of rigorous analysis, NASA confirmed yesterday that a rock sample collected by the Perseverance rover in Jezero Crater contains a potential biosignature, representing the strongest indication to date of the existence of ancient microbial life on Mars. This significant finding, detailed in the scientific journal Nature, focuses on a sample named "Sapphire Canyon," drilled from a rock known as "Cheyava Falls" back in July 2024.

A potential biosignature, as defined by scientists, is a substance, structure, or pattern that could have a biological origin but requires additional, more detailed analysis to completely rule out all non-biological (abiotic) possibilities for its formation. The "Sapphire Canyon" sample has now become the leading candidate in the mission's search for life, opening a new, exciting chapter in the exploration of Mars.

Traces of life in an ancient riverbed

The Perseverance rover, a tireless wheeled explorer, encountered the "Cheyava Falls" rock while investigating the "Bright Angel" geological formation. This formation features fascinating rocky outcrops located on the edges of the ancient river valley, Neretva Vallis. This is a canyon about 400 meters wide, through which vast quantities of water flowed billions of years ago, emptying into Jezero Crater and forming a delta that is now the primary target of research. It is believed that such environments, rich in water and sediments, were ideal for the development and preservation of traces of life.

Initial analyses by the rover's instruments revealed that the sedimentary rocks of the "Bright Angel" formation are composed of clay and silt. On Earth, these types of rocks are known as extraordinary archives of the past because they have the ability to preserve the fossilized remains of microorganisms. However, what particularly intrigued the scientists was the rock's chemical composition – a richness of organic carbon, sulfur, oxidized iron (rust), and phosphorus. According to Joel Hurowitz from Stony Brook University, the lead author of the study, this very combination of chemical compounds could have provided a plentiful energy source for the metabolism of ancient microbes.

The mystery of the "leopard spots"

The key moment in the investigation occurred when Perseverance's advanced instruments, PIXL (Planetary Instrument for X-ray Lithochemistry) and SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics and Chemicals), examined the "Cheyava Falls" rock in greater detail. On the reddish surface of the rock, measuring approximately one meter by 60 centimeters, unusual, colorful spots were observed. Further high-resolution analysis revealed that these spots, which the team named "leopard spots," are not random. They form a clear pattern of minerals distributed along so-called reaction fronts – lines of contact where intense chemical and physical reactions took place.

A detailed chemical analysis of these spots revealed the presence of two key iron-rich minerals: vivianite (hydrated iron phosphate) and greigite (iron sulfide). Their presence is extremely significant. On our planet, vivianite is often found in sediments, swamps, and around decaying organic matter, while certain types of microbes on Earth actively produce greigite as part of their metabolic process. The combination of these two minerals suggests they were formed as a result of electron transfer reactions between sediments and organic matter. It is precisely such reactions that microbes use to produce the energy needed for growth and life. This mineral assemblage, therefore, represents a potential fingerprint of ancient life.

Ruling out non-biological explanations

The scientific process demands extreme caution, so the team had to consider the possibility that vivianite and greigite were formed abiotically, without the involvement of living organisms. Such processes are possible, but they usually require specific conditions, such as prolonged exposure to high temperatures, extremely acidic conditions, or binding through certain organic compounds. However, the geological analysis of the rocks in the "Bright Angel" formation shows no evidence that they were exposed to extreme heat or an acidic environment.

Although it remains unknown whether the organic compounds present could have catalyzed the reaction themselves at low temperatures, the lack of evidence for other abiotic mechanisms makes a biological origin a more likely explanation. Katie Stack Morgan, the project scientist for the Perseverance mission at NASA's Jet Propulsion Laboratory (JPL), emphasizes that claims in astrobiology, especially those about the discovery of extraterrestrial life, require extraordinary evidence. Publishing the results in a peer-reviewed journal is a crucial step that ensures scientific rigor and validity. While abiotic explanations cannot be entirely ruled out, this study makes them less likely.

Implications for the history of Mars

The discovery also surprised scientists because it involves some of the younger sedimentary rocks the mission has explored so far. Previous hypotheses had largely assumed that signs of ancient life, if they exist, should be sought exclusively in the oldest geological formations. This finding suggests that Mars may have been habitable for much longer or at a later period in its history than previously thought. This opens up the possibility that older rocks also contain traces of life, which may just be harder to detect.

For the purpose of objectively evaluating such discoveries, the scientific community uses tools like the CoLD (Confidence of Life Detection) scale. This scale helps scientists assess how confident they are in their findings and what next steps are needed for confirmation. "Sapphire Canyon" is now high on that scale, but final confirmation will depend on future, even more sophisticated analyses.

The future of the samples: Return to Earth

"Sapphire Canyon" is one of 27 rock samples that Perseverance has diligently collected since landing in Jezero Crater in February 2021. These precious samples are stored in hermetically sealed titanium tubes and are awaiting the historic Mars Sample Return mission. This is a joint project of NASA and the European Space Agency (ESA) aimed at bringing these samples to Earth. Only analysis in the world's most advanced laboratories, with instruments too large and complex to be sent to Mars, will be able to provide a definitive answer to the question of whether the "leopard spots" truly hold the secret of ancient Martian life. The Perseverance mission, managed by JPL for NASA, continues its exploration of the Red Planet, not only in search of life but also collecting data on weather conditions and testing materials for spacesuits, thus preparing the way for future human missions.