On September 10, 2025, NASA announced that a rock sample from its Perseverance rover holds potential biosignatures. The same day, the journal Nature published the study behind the claim [1]. The lead author is Joel Hurowitz of Stony Brook University, writing with a large rover team.
NASA’s acting administrator, Sean Duffy, called it “the closest we have ever come to discovering life on Mars” in the agency’s release.
My reading is more careful. A potential biosignature is a reason to look harder, not a discovery of life. The paper itself says so, and the best chance at a final answer sits in a sample tube on Mars.
Where did Perseverance find this rock?
Perseverance landed in Jezero Crater in February 2021. In July 2024, it was exploring a group of rocks called the Bright Angel formation. According to NASA’s announcement, these rocks line Neretva Vallis, an ancient river valley about 400 meters wide. Long ago, water rushed through it into the crater.
One rock there stood out. Nicknamed Cheyava Falls, it is shaped like an arrowhead and measures about 1 meter by 0.6 meters. The rover drilled a core sample from it, named Sapphire Canyon, and stored it in one of its sample tubes.
The rock is a mudstone, which is mud that hardened into stone. NASA notes that on Earth, rocks made of clay and silt are excellent at preserving signs of past microbial life. The Bright Angel rocks are also rich in organic carbon, sulfur, rusty iron and phosphorus.
What are the leopard spots?
Cheyava Falls has small spots that the team calls leopard spots. Each has a dark rim and a lighter center, and they range from about 0.2 to 1 millimeter across. Even smaller dark specks, nicknamed poppy seeds, are scattered through the mudstone.
The rims and the poppy seeds are rich in iron phosphate, likely a mineral called vivianite. The centers of the leopard spots hold an iron sulfide, likely a mineral called greigite.
The spots are not lined up in layers, and their shapes are irregular. So the authors say they were not laid down as grains. Instead, they appear to have formed inside the rock after the mud settled. The rock’s setting and structure point to low temperatures.
One more pattern stood out among the rocks the team analyzed. Where the rover found the strongest organic signal, the rock was the least red and held the most of these minerals. Where it found no organic matter, the rock was the reddest and held the least.
How could the spots have formed?
The authors propose a simple story. Red rock gets its color from rusty iron. In wet mud, organic matter can react with that iron and turn it into a form that dissolves in water. That frees iron and phosphate, which can then come together as vivianite. A similar reaction with sulfate, a sulfur compound, could make the iron sulfide. In this picture, the reactions also bleached the red color out of the mud, more so where there was more organic matter. That fits the lighter centers of the spots.
On Earth, microbes run these same reactions to get energy. Vivianite nodules form in fresh water and in the sea as a by-product of iron reactions run by microbes. Some microbes also make iron sulfides like greigite. “The combination of chemical compounds we found in the Bright Angel formation could have been a rich source of energy for microbial metabolisms,” Hurowitz said.
Imagine finding a dark ring on your kitchen counter. A wet coffee mug could have left it. So could a hot pan. The ring alone cannot tell you which, so you need more clues before you decide.
That is where scientists stand with Cheyava Falls. The ring is real, but what left it is still an open question.
Why can’t scientists just say it is life?
The same minerals can form without any life at all. The paper takes this seriously [1]. The authors first test a null hypothesis, which is the default explanation scientists check before anything else. Here, that means ordinary chemistry, with no life involved, made the minerals in the spots.
Many organic compounds can dissolve rusty iron without life, at temperatures between 10°C and 80°C. The paper says the organic matter in this rock suggests such reactions could have happened. That organic carbon might not be biological either. It could have formed on Mars through chemistry, or come from nonbiological sources beyond the planet. The authors say more work must show whether this rock’s own organic compounds can do this at low temperatures.
Other nonliving routes face problems, the paper says. Without life, organic matter turns sulfate into sulfide extremely slowly unless the rock gets hotter than about 150°C to 200°C. The authors found no clear sign that these rocks were ever heated that much. NASA adds that the rocks show no sign of acidic conditions, another nonliving route.
Katie Stack Morgan is Perseverance’s project scientist. Abiotic means without life. “And while abiotic explanations for what we see at Bright Angel are less likely given the paper’s findings, we cannot rule them out,” she said.
What does potential biosignature really mean?
NASA’s definition is short. A potential biosignature “might have a biological origin but requires more data or further study” before anyone can decide whether life was present.
The paper uses a fuller definition. It describes a feature that fits with life but challenges researchers to decide between living and nonliving causes. It also pushes them to gather more data before they conclude anything. In other words, the label is a to-do list, not a verdict.
I think Cheyava Falls is one of the strongest leads yet in the search for past life on Mars, and the team handled it honestly. But the closest we have come is not the same as close. Until a lab on Earth tests the sample, this is chemistry that looks like life.
So I read the Duffy quote as true but easy to misread. Nicky Fox, who leads NASA’s science missions, put it better. She said NASA was sharing the data so other scientists could “confirm or refute its biological potential” through further study.
Why does the sample need to come to Earth?
A rover must carry every tool it uses. Labs on Earth have no such limit. The authors conclude that sensitive instruments on Earth can make the measurements needed to trace where the minerals and organics came from.
In January 2025, NASA said it would study two ways to land the spacecraft that would pick up the samples. The plan was to load 30 sample tubes into a container. A European Space Agency spacecraft would then catch it in orbit around Mars and bring it back. NASA expected to confirm the program and its design in the second half of 2026. So as of that release, the ride home was still only a plan.
How should we read news like this?
When a headline says a rover found signs of life, look for the word potential. Then ask two things: what nonliving explanation is still possible, and what test would settle it?
For Cheyava Falls, the paper answers both. Ordinary chemistry has not been ruled out, and the team says Earth labs offer the best test. I trust the study more because the team spelled out what could still prove them wrong. For now, the honest answer is that we do not know yet.
References
[1] J. A. Hurowitz, M. M. Tice, A. C. Allwood, M. L. Cable, K. P. Hand, A. E. Murphy, et al., “Redox-driven mineral and organic associations in Jezero Crater, Mars,” Nature, vol. 645, no. 8080, pp. 332-340, Sep. 2025, doi: 10.1038/s41586-025-09413-0.
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