Two minerals, known almost exclusively to be linked with microbial metabolism, have been found in a recent drill sample by the Perseverance rover.
They sparked a flurry of excitement, and NASA Acting Administrator Sean Duffy was quick to point out that gold-standard science will need to be performed on what he called “the closest we have ever come to discovering life on Mars.”
The hype comes entirely from the presence of two minerals: vivianite and greigite.
Per the Mineralogical Society of America, greigite is formed by magnetotactic bacteria and sulfate-reducing bacteria in lake soils or hydrothermal vents. It’s one of several materials scientists have theorized could have acted as a catalyst for the origin of life, in part because a certain iron-based unit of greigite is present in a protein needed to drive the acetyl-COA pathway—a foundational metabolic process.
Vivianite is a hydrated iron phosphate mineral found in fossils, bivalve and gastropod shells, and in human graveyards and coffins; the result of a chemical reaction of the decomposing body with the iron enclosure. Sharp-eyed readers may think that the “vivi” in vivianite comes from the word for life, but it’s actually named after a scientist called John Henry Vivian.
Both vivianite and greigite were found in a recent core sample taken at Neretva Vallis, an ancient river channel about a quarter mile-wide that once fed the lake at the bottom of Jezero Crater, the site where Perseverance began its search for microbial life more than 5 years ago.
“This finding by Perseverance is the closest we have ever come to discovering life on Mars. The identification of a potential biosignature on the Red Planet is a groundbreaking discovery, and one that will advance our understanding of Mars,” said acting NASA Administrator Sean Duffy.
“NASA’s commitment to conducting Gold Standard Science will continue as we pursue our goal of putting American boots on Mars’ rocky soil.”
The reference to American boots isn’t just hyperbole. The recent NASA budget was directly tied to a human mission to Mars, and it included the canceling of a potential billion-dollar sample return mission that would have collected the Neretva Vallis cores, among dozens more, that Perseverance has cached across the landscape.
Instead, NASA has decided that rather than investing so much on a never-before-attempted mission, it would be far more straight forward to have astronauts collect them by hand.
Earth.com reports that the sample sediments showed a ring of vivianite penetrated by small “leopard spot” cores enriched in greigite, a pattern that matches a sequence seen in biologically mediated vivianite through the influence of extracellular electron transfer, another fundamental metabolic pathway, that has been documented in biologically-live Earth sediments.
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None of this proves the Neretva Vallis samples were made by microbes, but it’s certainly the closest scientists have ever come to detecting evidence of life.
The discovery, whether it proves to be life or not, does extend the period during which Mars was potentially habitable (or not) to at least as far forward in the planet’s history as when this river channel was wet, an important reference date for future studies.
With such a strong biosignature being found within 6 years of exploration, there’s every chance other such mineral cycling evidence will be uncovered in future samples or missions, which in turn could be informed by the conclusions drawn from these core samples.
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The big question will be whether or not scientists can demonstrate that greigite and vivianite need biological life to form, or can they do so a-biotically. Alternatively, is there some signature that biotic greigite and vivianite will always carry that a-biotic versions do not?
The answers to those questions will be the most impactful ones perhaps ever made in the quest to discover whether Mars was habited by microbes once upon a time.
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