Since February 2021, NASA’s Perseverance rover has been exploring a region on Mars known as Jezero Crater, a huge cavity believed to have once hosted a lake. It’s considered one of the most promising places to look for evidence of ancient life on the Red Planet (life as we know it, at least) — and there has been an update in the search.
On Wednesday (Sept. 10), researchers presented a study that describes how Perseverance found intriguing minerals on the western edge of Jezero Crater, in the clay-rich, mudstone rocks of a valley called “Neretva Vallis.” Here on Earth, these minerals are typically associated with organic matter. So, could this mean we’ve finally found proof of aliens? Well, not quite. The authors stress that further analysis is necessary to identify the true origin of the minerals and determine whether they are indeed markers of life, otherwise known as “biosignatures,” or the result of some other inorganic processes.
Either way, the findings do demonstrate that notably complex reactions once occurred on Mars — organic or not — adding yet more layers to the planet humans have been trying to decode since the dawn of astronomy.
To get into some specifics, the samples Perseverance collected that appear to harbor those exciting minerals were found in what’s known as the “Bright Angel” formation within the northern margin of Neretva Vallis. Within that formation, one particular rock is of great interest to researchers. It’s named “Cheyava Falls.”
Not too long ago, when Cheyava Falls was first presented to the public, it made headlines around the world because scientists were openly fawning over the specimen’s peculiar, dotty features that resembled “poppy seeds” and “leopard spots.” The latter, which are millimeter-size blobs, are each surrounded by black rings that scientists determined contain iron and phosphate after studying them with Perseverance’s toolkit. Both substances can result from chemical processes on Earth that are driven by microbes.
“These spots are a big surprise,” David Flannery, an astrobiologist and member of the Perseverance science team from the Queensland University of Technology in Australia, said at the time. “On Earth, these types of features in rocks are often associated with the fossilized record of microbes living in the subsurface.”
The natural next step was to have Perseverance examine Cheyava Falls (and other specimens associated with Bright Angel) a little more closely. On July 21, 2024, the rover even drilled into Cheyava Falls and collected a sample. This sample, the 25th that Perseverance had grabbed, is named Sapphire Canyon.
“I would describe the Sapphire Canyon sample as mysterious,” Morgan Cable, a research scientist for Perseverance, previously said in a video about the core sample that NASA posted on April 10. “We see these signatures that tell us chemistry has happened, potentially involving organics — but what does that mean? Could life have been involved, or something that didn’t involve life at all?”
That’s sort of where the tale left off.
Now, what the new study appears to add to the story is a very detailed analysis of the Bright Angel bunch. Sure enough, the researchers found evidence that this outcrop really could be a solid lead in the quest to find proof of life beyond Earth. According to a release about the results, the team “identified tiny nodules and specks enriched in iron phosphate and iron sulfide. These features are associated with organic carbon and appear to have formed after sediment deposition, under low-temperature conditions.”
The key seems to be the result that certain “redox” reactions could have occurred to give rise to these minerals. A redox reaction is a chemical reaction in which electrons are transferred between two substances; one of the substances is oxidized and the other is reduced.
“This organic carbon appears to have participated in post-depositional redox reactions
that produced the observed iron-phosphate and iron-sulfide minerals,” the study authors write.
“The exciting discovery of reduced iron phosphates and sulfides associated with organic compounds in the clay-rich mudstones of Jezero Crater suggests that the organic material might have been involved in the unusual redox reactions,” states a News and Views article, written by Janice Bishop of SETI Institute in Mountain View, California and Mario Parente of the University of Massachusetts, Amherst. This article was published in tandem with the study results.
“On Earth, microorganisms commonly interact with minerals and have been observed to convert sulfates (which contain oxidized sulfur atoms) to sulfides (which contain reduced sulfurs) in cold, oxygen-free Antarctic lakes,” the News and Views article continues. “There is no evidence of microbes on Mars today, but if any had been present on ancient Mars, they too might have reduced sulfate minerals to form sulfides in such a lake at Jezero crater.”
A few other results presented in the team’s paper strengthen the case of a possible biosignature existing in Mars’ Bright Angel formation as well. For instance, the new findings suggest the green-toned specks in muddy clay found in the outcrop could contain the mineral vivianite, which the News and Views authors say can specifically shed light on certain kinds of redox reactions that may have taken place on Mars.
All in all, however, there is one major underlying elephant in the room: For any further confirmation of whether evidence of Mars life lies in Perseverance’s sample tubes, those sample tubes need to be returned to Earth. Unfortunately, as of now, NASA’s Mars Sample Return program remains in limbo due to budget constraints, priority shifts since the Trump administration took the White House and a highly complicated blueprint for the mission.
Still, scientists continue to stress that there is only so much one can do when analyzing tiny rock samples while separated by a 140-million-mile (225-million-kilometer) stretch of the vacuum of space.
“Ultimately, the return of samples from Mars for study on Earth, including the Sapphire Canyon sample collected from the Bright Angel formation, would provide the best opportunity to understand the processes that gave rise to the unique features described here,” the study authors write.
“Laboratory analyses of samples returned from Mars could also cast light on the potential for prebiotic — and even biological — chemistry to occur on worlds beyond Earth,” the News and Views authors write.
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