The Perseverance Rover May Have Found Past Signs Of Life On Mars

A speckled sample of rocks discovered by the Perseverance rover at the Jezero Crater site on Mars exhibits characteristics that, if found on Earth, would be considered evidence of past living microorganisms. An article appearing in the journal Nature, on September 10, 2025, describes the rocks and what appear to be embedded biosignatures.

Perseverance, since landing on Mars, has explored three of the geological terrains in the Jezero Crater. These are the crater floor containing lava flows and water-deposited rocks, a delta fan with fluvial deposits, and the crater margin, where mudstone, carbonate rocks and olivine deposits have been found.

Finding mudstone on Mars has always excited astrobiologists. Mudstone only forms where water and silt are present to produce hardened sediments. It forms from the compaction of fine particles. Carbonate rocks also form in the presence of water, producing limestone, calcite and dolomite. On Earth, carbonate rocks often contain minerals formed from the skeletal remains of animals.

Olivine, on the other hand, doesn’t form in the presence of water but rather reacts to water and carbon dioxide (CO2), generating a chemical exothermic response that could support organic molecules and biotic chemistry. Its presence on Mars is considered an indicator of long, dry and cold periods in the planet’s history.

Olivine discoveries on Mars have interested exobiologists because of a process called serpentization, where exposure to water transforms it, even in low-temperature environments. When serpentization happens to olivine through interaction with a water source, the altered rock turns into secondary minerals while producing byproducts like hydrogen gas and heat.

On Earth, serpentization is observed on the edges of tectonic plates. On Mars, however, olivine has a complex history, with changes in its appearance indicating limited interactions with liquid water in the past during periods that would have been favourable to life.

The rocks that have the astrobiologists excited were observed and collected by Perseverance from a mudstone outcrop called Cheyava Falls. It was once a river channel or ancient lake delta. The sample features complex mineralogy, layered sediments,  and chemical biosignatures. This is the most promising sample found by Perseverance, which, along with Curiosity, was sent to Mars to find past environments that could have been conducive to life.

NASA has chosen to seek environmental evidence to support life, rather than evidence of life itself. Why is that? The likely explanation is the controversy that arose when the two Viking landers reached Mars in 1976.

On board the Vikings was the Label  Release Experiment (LRE). It tested soil samples dug up using a trenching tool. The samples were deposited in the onboard chemical lab, where they underwent several tests, one of them the LRE.

The LRE was conducted in two stages. The first stage introduced an unheated soil sample to a diluted aqueous solution containing seven molecular compounds tagged with radioactive carbon-14 to track metabolic activity. The nutrients included glycine, alanine, sodium formate, sodium lactate, and calcium glyconate. The test measured the gasses emitted from the sample. A second sample was heated to 160 °C (320 °F) with the gas output measured. On Earth, the two-stage experiment was repeated using terrestrial soil samples. All four results were compared. A positive test for metabolic activity, indicating the possibility of Martian life, produced radioactive carbon-labelled gasses.

But the Viking also had another onboard test, the Pyrolytic Release Experiment, which exposed collected soil samples to light, water and radioactive carbon-14, looking for photosynthetic activity. The results showed no organic material was present.

As with all things at NASA, the interpretation of the conflicting results led to the downplaying of the LRE, erring on the side of caution. Many scientists, 50 years later, however, believe that upon reviewing the Viking data, the landers did find evidence of past and maybe even present active microbial life on Mars. Over the years since 1976, the certainty by astrobiologists of past or present life on Mars has grown to 99%. Considering the organic compounds found by both Curiosity at the Gale Crater and Perseverance at Jezero, their judgment seems well-founded.

So why does NASA continue to tiptoe around the question of life on Mars? The best explanation is that, without holding the physical evidence in hand, the discovery of life on Mars remains unanswered. In NASA’s defence of timidity, when you consider that human activities on Mars have only sampled a small portion of the planet’s surface, there appears to be a lot more exploration to do. The proof of Martian microbial life, I believe, will become a reality when humans finally land on Mars to explore more environmentally suitable niches on and below the surface. That level of commitment, however, to planetary science rather than to bragging rights, seems far away.

Could abiotic processes have produced the Viking results or refute the visual evidence that Perseverance has encountered? Most planetary scientists and astrobiologists don’t believe that an abiotic interpretation is more likely. They do, however, cautiously note it cannot be totally excluded.

What is needed is getting the Perseverance Martian test samples back to Earth. That was to be the goal of the future Mars Sample Return Mission. It appears, however, that it may no longer happen with plans to cut NASA’s science budget. Instead, we may have to wait until human crews land on Mars and observe and test the rocks and soil they sample.