Mars hasn’t given us proof of life, but it surely has handed scientists a brand new form of thriller.
On the western fringe of Jezero Crater, NASA’s Perseverance rover has been exploring Neretva Vallis, a river-carved valley that when fed an unlimited Martian lake. There, in an outcrop of historical mudstone referred to as the Bright Angel formation, the rover discovered certainly one of its most intriguing targets but: an arrowhead-shaped rock nicknamed Cheyava Falls, flecked with tiny black “poppy seeds” and ringed “leopard spots.”
Closer evaluation revealed that the unusual markings are wealthy in natural carbon, iron, phosphorus and sulfur. More strikingly, scientists recently reported signs of vivianite (an iron phosphate) and greigite (an iron sulfide). On Earth, both minerals typically form through redox reactions — the electron-swapping processes that underpin all life. Plants rely on redox in photosynthesis, humans and other animals use it to extract energy from food during respiration, and microbes employ it to “breathe” metals in oxygen-starved settings such as deep-sea vents.
On our planet, such signatures are often the fingerprints of biology. On Mars, they remain a tantalizing “maybe” — chemical traces that could point to life, or could also arise from purely non-living processes. Either way, they mark a departure from the chemistry that scientists are used to seeing on the Red Planet.
“Whatever their origin, this is a very distinct chemistry than anything we’ve seen in ~20-25 years of roving the planet,” Joel Hurowitz, a geoscientist at Stony Brook University in New York who led the recent study, told Space.com.
Even if the reactions grow to be non-biological, he added, they may reveal “prebiotically useful chemistry we haven’t thought about before,” whereas additionally serving as a reminder of the ways in which abiotic nature can mimic life’s indicators — false positives for biosignatures “that we’ll have to do some really hard thinking about.”
A window into Mars’ previous
Mars’ floor normally tells a narrative of oxidation: iron reacting with oxygen billions of years in the past, when liquid water and a thicker environment had been nonetheless current, forsaking the worldwide blanket of rust that earned Mars its enduring nickname, the Red Planet. At Cheyava Falls, nonetheless, Perseverance recognized minerals that shaped via the opposite half of the equation, often known as discount, the place iron and sulfur gained electrons as a substitute of shedding them.
Redox reactions are particularly compelling as a result of, left to themselves, they proceed solely sluggishly at low temperatures. That sluggish tempo, and the vitality locked inside it, makes them a wonderful gasoline supply for all times. Life fast-forwards these reactions with enzymes, enabling microbes to grab the vitality that might in any other case dissipate.
“All living things need to get energy from their environment. Life on Earth figured out how to do that very early by taking advantage of redox reactions,” research co-author Mike Tice, a geobiologist at Texas A&M University in College Station, advised Space.com.
Seeing proof of redox chemistry on Mars, then, raises the chance that comparable processes might as soon as have supported any life which will have emerged there.
That’s what makes the minerals Perseverance spotted — particularly greigite in the leopard spots — so compelling. Abiotic sulfide production at low temperatures is extremely sluggish, according to Tice.
“They basically don’t happen at the temperatures that we think these rocks experienced,” he said. “So, the very things that make this particular redox reaction useful to some living organisms are the things that make it useful as potential evidence for life.”
With rocks more than 3.5 billion years old, non-biological processes have had plenty of time to leave behind features that mimic biosignatures. At Cheyava Falls, though, the rocks show no signs of being altered by heat or pressure that could have driven fast chemical reactions, yet sulfides are present in notable amounts. For scientists, that discrepancy keeps open — but does not confirm — the possibility of a biological origin.
“It’s very indirect evidence for life,” Chris Impey, an astronomer at the University of Arizona who was not involved in the study, told Space.com. “It’s not going to convince anyone that there’s life on Mars beyond a reasonable doubt, which is at this point where the game is.”
Gerard van Belle, the director of science at Lowell Observatory in Arizona, who was additionally not concerned within the research, agreed. “It’s not a smoking gun,” he advised Space.com. “The $100,000 question here is, Are those things something that would come from a uniquely biotic source, or are there abiotic ways?”
Still, these redox reactions intrigue scientists as a result of they go away behind minerals that act like time capsules. Their chemistry and abundance protect clues in regards to the atmosphere by which they shaped — whether or not water as soon as moved via the rocks, how oxygen-rich or oxygen-poor the atmosphere was, and whether or not vitality sources existed that microbes may need tapped.
The Bright Angel mudstone additionally appears chemically distinct from different Jezero rocks. It is unusually oxidized and stripped of components like magnesium and calcium, a profile that Hurowitz mentioned resembles soils on Earth which have been closely weathered by lengthy publicity to rain. That distinction doubtless displays shifts in Mars’ local weather and environment as Jezero Crater full of sediment, the researcher mentioned.
“The Bright Angel formation adds new dimensions to the overall picture of Mars’ past environments,” Hurowitz mentioned. It tells scientists that the planet’s local weather and environment might have assorted significantly via time, “but also [have been] capable of supporting habitable environments while all of that variation was occurring.”
Perseverance has already drilled a core from Cheyava Falls and cached it for eventual return to Earth. If all goes to plan with NASA’s Mars Sample Return (MSR) mission marketing campaign, scientists are keen to research the rock in methods inconceivable aboard the rover. (That’s removed from assured, nonetheless; MSR has been stricken by delays and value overruns, and President Donald Trump’s 2026 proposed federal finances would cancel the mission.)
Hurotwiz mentioned he would “want to go right to work” on isotopic measurements of the Cheyava Falls pattern — evaluating lighter and heavier variations of iron, sulfur and carbon within the rock, notably between the unique mudstone and the newer minerals, vivianite and greigite, that crystallized inside it. Differences in isotopic compositions between these reactants and merchandise, he famous, “can be diagnostic in determining whether or not biology was involved in the redox reactions that formed them.”
Van Belle mentioned that returning pristine samples to Earth would make “a big difference” within the seek for fossil-like buildings — the form of proof that has lengthy fueled debates, reminiscent of these over the well-known Mars meteorite Allan Hills 84001, however this time with out the uncertainty of contamination.
Tice mentioned that, if somebody had requested him two years in the past whether or not life ever existed on Mars, his reply would have been that scientists merely did not know sufficient to have a significant dialogue. Previous NASA missions had proven that the Red Planet’s floor might have supported life billions of years in the past however did not provide proof for or in opposition to its habitation throughout that point.
Now, Perseverance is starting to alter that.
“We now have the first hints,” he mentioned, “and we can have real arguments and plan new observations constrained by the reality of actual rocks and minerals — that excites me!”
He likened the second to treasure looking. “This is the moment where the metal detector has gone off and you’ve dug up something shiny,” he mentioned. “You still need to find out exactly what you’ve got — but you’ve got something to work with.”