This is the best evidence yet for ancient life on Mars
NASA’s Perseverance rover found possible signs of ancient life in rocks on Mars, keeping scientists up at night.
Geologist Michael Tice had never lost sleep over a Mars rock before. That changed as he dug into data from the red planet’s Bright Angel rock formation, located in an ancient river valley called Neretva Vallis.
This rock formation contains the most compelling evidence to date for possible ancient life on Mars, based on a new analysis of rocks explored by NASA’s Perseverance rover published September 10 in the journal Nature.
The result “is the closest we've actually come to discovering ancient life on Mars,” Nicola Fox, associate administrator for science at NASA, said at a press conference.
Further research is needed to confirm that life indeed existed there, but for scientists like Tice and his collaborator Joel Hurowitz, the rocks of Bright Angel raise the possibility that microbes thrived in the mud underwater some 3.5 billion years ago.
(First active fault zone found on Mars)
“It's pretty mind blowing,” says Tice, a research scientist at Texas A&M University and co-author of the new study. “When Joel and I started seriously considering the possibility that life could have been involved in forming these things, I had trouble sleeping that night.”
Bright Angel’s rocks, on the western edge of Jezero Crater, were likely deposited at the bottom of a lake or river when water flowed freely on a planet that is now dry. Chemical clues in a rock nicknamed Cheyava Falls suggest that a specific type of reaction occurred that, on Earth, typically involves microbial life.
“This is the first time that chemical processes consistent with—though not definitive proof of—a biological origin have been observed” on Mars, says Christian Schröder, a physicist at the Max Planck Institute for Solar System Research, who was not involved in the study.
Poppy seeds and leopard spots
Throughout Bright Angel, Perseverance found greenish specks scientists like to call “poppy seeds” or “nodules” embedded in reddish mudstone. Prominent in those specks is the mineral vivianite containing iron phosphate.
Cheyava Falls also contains tiny, ring-like features called “leopard spots.” The rover drilled a thin rock core sample, barely as long as an adult pinky finger, and used its suite of science instruments to learn more. Data from the sample, dubbed Sapphire Canyon, now reveals that the rims around the spots are also made of dark, iron phosphate minerals, and lighter interior areas are made of an iron sulfide mineral called greigite.
(Learn about other Mars rocks aiding the search for life.)
What’s most exciting for the search for life would have occurred at a scale even smaller than molecules. In an oxidation-reduction or “redox reaction,” organic material gave over electrons to iron in the mud and left these other minerals, vivianite and greigite, behind.
On Earth, microorganisms spark reactions like this by consuming the organic matter and capturing the energy released in the redox process, with minerals formed as byproducts. It’s like kind of like how humans eat food to gain energy, and generate waste, too.
“The places where we see that happening on Earth, in ambient-temperature, sedimentary settings, those reactions are typically driven by microbes,” says Hurowitz, a geologist at Stony Brook University.
If the Cheyava Falls results ultimately do lead to the proof of ancient life on Mars, Tice notes, that means two different planets hosted microbes getting their energy through the same means at about the same time in the distant past. That could suggest that early life learns how to survive in this way regardless of where it originated. “I think that could be telling us something really profound about how life evolves,” he says.
How to prove it was life
Proving that a sign of life, or what scientists call a biosignature, has been found definitively is an enormous scientific undertaking. It requires multiple lines of evidence, from different scientific instruments, and a thorough investigation of the geological context in which the biological signal could have been produced. Enormous amount of scrutiny and debate would ensure before such a ground-breaking conclusion.
The obvious first question is: Can a non-biological source produce the same result?
The same redox reactions described in the Mars rock paper, with the same byproducts, can occur without the presence of life, but only under hot conditions. A volcanic eruption could theoretically explain something like this, no life required. But the study authors believe conditions weren’t hot enough in this particular location when the rocks seem to have been underwater.
“If you were to take the mud and the organic matter and cook them, you could come up with that same set of minerals,” Hurowitz says. “But so far, using all the tools available to us, we don't see any evidence that these rocks were heated up to the kinds of temperatures that would be needed to make that reaction happen.”
What’s more, Tice noted that if a massive lava flow event had created the leopard spots they would only appear in a single layer, rather than multiple layers of the core sample.
Scientists stressed that to know for sure whether ancient microbial life was responsible for the poppy seeds and leopard spots in Sapphire Canyon, samples of Mars rocks would need to be returned to Earth so that scientists can use more sophisticated laboratory equipment to more thoroughly investigate. The fate of NASA’s own sample return program remains up in the air, however.
In the meantime, the European Space Agency’s Rosalind Franklin rover could also push the story of life on Mars forward. It will drill deeper into the red planet’s surface and analyze samples on the red planet. Samples from farther underground would be better preserved from the harsh surface environment, notes Schröder, who is affiliated with the project. Named for a key collaborator in the discovery of the DNA double helix, ESA’s rover is expected to launch in 2028. China also hopes to launch a sample return mission around the same time
To rule out explanations other than life, scientists need to also explore more environments on Earth that have characteristics similar to those of ancient Mars, Hurowitz says, to see if there are examples of similar chemical reactions happening without the involvement of biology. These could include the bottoms of lakes, estuaries, and other areas where rocks are immersed in water.
(Why signs of life on Mars remain so mysterious)
Is this the first possible evidence of life on Mars?
NASA first announced the discovery of the arrowhead-shaped rock Cheyava Falls, named for the tallest waterfall in the Grand Canyon, in July 2024. With white veins of calcium sulfite, the rock had chemical signatures and structures that, billions of years ago, could have been forged by life. Those included carbon-based molecules fundamental to biology, but which could also come from non-biological sources.
This isn’t the first time that a Mars rover has found possible signs of ancient habitability and conditions that could point to life. NASA's Spirit rover, for example, found an ancient hot spring environment at Gusev Crater before getting stuck in sand and losing contact. The Curiosity rover, which is still operating today at Gale Crater, found organic compounds in mudstones there.
But telltale signs of redox reactions elevate this new finding above the environmental clues that other Mars rovers have found, Schröder says.
As for whether Cheyava Falls is the most interesting rock beyond Earth, Hurowitz hesitates, but adds, “if your specific interests are astrobiology and geobiology, this is a pretty darn good candidate for favorite rock.”
