Has it finally happened? Has NASA finally found biosignatures from ancient Martian life? It's too early to reach that conclusion, but the Perseverance Rover did find chemical compounds that microbes could've used as an energy-rich food. They also found minerals that could've been created by biological reactions.
The findings are in new research in Nature titled "Redox-driven mineral and organic associations in Jezero Crater, Mars." The lead author is Joel Hurowitz of Stony Brook University, who is also a Perseverance scientist.
In July 2024, Perseverance was exploring a region near Jezero Crater named Bright Angel. Bright Angel is a section of rocky outcrops near the ancient river valley Neretva Vallis.
"Upon entering Neretva Vallis, on Jezero Crater’s western edge, Perseverance investigated distinctive mudstone and conglomerate outcrops of the Bright Angel formation," Hurowitz and his co-authors write in their research. While exploring Bright Angel, Perseverance came across several interesting rocks, including one named after a waterfall in the Grand Canyon, Cheyava Falls, and another named Apollo Temple. Perseverance analyzed both rocks.
"Here we report a detailed geological, petrographic and geochemical survey of these rocks," the authors write.
The region contains ample clay and silt, which on Earth are known to preserve evidence of microbial life. When Perseverance analyzed the rocks, it found organic carbon, phosphorous, sulphur, and oxidized iron. Taken together, these chemicals could've been a source of nutrients for ancient microbes.
“The combination of chemical compounds we found in the Bright Angel formation could have been a rich source of energy for microbial metabolisms,” said lead author Hurowitz in a press release. “But just because we saw all these compelling chemical signatures in the data didn’t mean we had a potential biosignature. We needed to analyze what that data could mean.”
Intriguing featureson the surface of Cheyava Falls deepened the curiosity. The rock had spots that could've been left behind by microbes that had used the nutrients. Closer inspection showed that the spots, which the Perseverance team is calling Leopard Spots, contain minerals in a pattern called reaction fronts. Reaction fronts are locations where fluids moving through rock experience chemical reactions. This activity creates boundaries between altered and unaltered material.
The spots contain evidence of a pair of iron-rich minerals, vivianite (hydrated iron phosphate) and greigite (iron sulfide). On Earth, vivianite forms in low-oxygen environments like peat bogs, where it often replace organic materials. Greigite is found in sediments on Earth, and is formed by bacteria. But that's on Earth.
Electron transfers are at the heart of this issue. These are fundamental chemical processes in biological processes like photosynthesis. But they're also fundamental in non-living process like combustion and corrosion. The minerals in the Leopard Spots formed through electron transfers between sediment and organic matter. That means the spots are a potential biosignature for microbial life, but they can also originate abiotically.
This is where temperature comes in. For them to be produced abiotically, high temperatures, acidic conditions, and binding by organic compounds are needed. But the rocks in question show no evidence of high temperatures. They also show no evidence of acidic conditions, and the researchers don't know if the organic compounds Perseverance found can catalyze the required reactions at low temperatures.
"This organic carbon appears to have participated in post-depositional redox reactions that produced the observed iron-phosphate and iron-sulfide minerals. Geological context and petrography indicate that these reactions occurred at low temperatures," the researchers explain in their paper.
In another twist, the rocks in question are relatively young. In general, scientists think that any life on Mars existed when the planet was warm and wet in its distant past. But the youthfulness of these rocks could upend that notion. If life was involved, it had to exist later in Martian history than thought.
For hundreds of years, scientists have urged us to keep an important idea in mind. Though others before him said it in different ways, Carl Sagan emphasized it most recently when he said "Extraordinary claims require extraordinary evidence."
So is there enough extraordinary evidence to say these are unambiguous biosignatures? Simply put, no there's not.
“Astrobiological claims, particularly those related to the potential discovery of past extraterrestrial life, require extraordinary evidence,” said Katie Stack Morgan, Perseverance’s project scientist at NASA’s Jet Propulsion Laboratory in Southern California. “Getting such a significant finding as a potential biosignature on Mars into a peer-reviewed publication is a crucial step in the scientific process because it ensures the rigor, validity, and significance of our results. And while abiotic explanations for what we see at Bright Angel are less likely given the paper’s findings, we cannot rule them out.”
Scientists have created a tool to determine how strong evidence of life is. It's called Confidence of Life Detection, or CoLD, and it's a scale containing seven benchmarks. CoLD is a way of ranking evidence based on how much confidence we should have in it.
The Perseverance rover is an astrobiology mission, and it carries instruments that allow it to examine rock in great detail, microscopically, chemically, and structurally. It's mission is to find evidence like this and study it to the extent of its capabilities. Ancient life on Mars is not going to announce itself. The evidence will likely be obscured like these findings are.
"In summary, our analysis leads us to conclude that the Bright Angel formation contains textures, chemical and mineral characteristics, and organic signatures that warrant consideration as ‘potential biosignatures’, that is, “a feature that is consistent with biological processes and that, when encountered, challenges the researcher to attribute it either to inanimate or to biological processes, compelling them to gather more data before reaching a conclusion as to the presence or absence of life," the authors write.
But this issue doesn't end here. When Perseverance was launched, it was partly a bet on the future. It was a gamble that NASA would sustain its interest in Mars. And it was a gamble on a future mission. Throughout its journey, the rover has collected core samples and cached them for later retrieval with an undefined future sample-return mission. One of Perseverance's core samples is from Cheyava Falls, and the sample is called Sapphire Canyon. If a sample return mission is ever executed, Sapphire Canyon will find its way to labs here on Earth.
Perseverance is a remarkable mission that's performing extremely well. It's delivering the kind of evidence that sober-minded scientists were hoping for. But the key to this evidence lies in returning the sample to Earth.
"Ultimately, we conclude that analysis of the core sample collected from this unit using high-sensitivity instrumentation on Earth will enable the measurements required to determine the origin of the minerals, organics and textures it contains," the authors write in their research.