Perseverance's PIXL Finds Vivianite, Greigite in 'Cheyava Falls' Sample

NASA's Perseverance Mars rover generated this mineral map showing the presence of two minerals – vivianite (purple and pink) and greigite (dull yellow and green) – on the surface of a rock nicknamed "Cheyava Falls." The data helped scientists determine the rock contained a potential biosignature, which is a substance or structure that might have a biological origin but requires more data or further study before a conclusion can be reached about the absence or presence of life. Perseverance's PIXL (Planetary Instrument for X-ray Lithochemistry) and SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals)instruments found a distinct pattern of minerals arranged into reaction fronts (points of contact where chemical and physical reactions occur) that the team called "leopard spots." The leopard spots carried the signature of vivianite (hydrated iron phosphate) and greigite (iron sulfide). Vivianite appears within black spots mission scientists refer to as "poppy seeds" and in the dark rims of the larger "leopard spots." Greigite is seen within the interiors of the leopard spots, which could have been left behind by microbial life if it had used the raw ingredients – the organic carbon, sulfur, and phosphorus – in the rock as an energy source. Vivianite is frequently found on Earth in sediments and peat bogs and around decaying organic matter. Similarly, certain forms of microbial life on Earth can produce greigite. The combination of these minerals, which appear to have formed by electron-transfer reactions between the sediment and organic matter, is a potential "fingerprint" for microbial life, which would use these reactions to produce energy for growth. The minerals can also be generated abiotically, or without the presence of life. https://photojournal.jpl.nasa.gov/catalog/PIA26640