Fe-phosphates in Jezero Crater as evidence for an ancient habitable environment on Mars

Phosphorus is an essential component for life, and in-situ identification ofphosphate minerals that formed in aqueous conditions directly contributestoward one of themain goals of theMars 2020 Perseverance rover: to seeksigns of ancient habitable environments. In Jezero crater, proximity scienceanalyses within a conglomerate outcrop, “Onahu” demonstrate the presenceof rare Fe3+-bearing phosphate minerals (likely metavivianite, ferrolaueite,(ferro)beraunite, and/or santabarbaraite) embedded in a carbonate-richmatrix.While Fe-phosphates have been inferred previously onMars, this workpresents the most definitive in-situ identification of martian Fe-phosphateminerals to date, using textural, chemical, spectral, and diffraction analyses ofdiscrete green-blue grains. The Fe-phosphate minerals’ textural context alongwith comparisons to Earth analogs suggest they likely formed after oxidationof Fe2+-phosphate vivianite, the most common Fe-phosphate in sedimentaryenvironments on Earth, often associated with microbial activity and organics.While there is no obvious evidence of biological inputs in Onahu, if the Fephosphates’formation environment was similar to vivianite-rich sedimentaryenvironments on Earth, these minerals likely originally precipitated in conditionsfavorable to potential martian life — in a low temperature, reducingaqueous medium with high concentrations of bio-limiting elements, and Feredoxgradients that could provide an energy source. If the sample collectedfromOnahu (Otis_Peak) is returned to Earth, analysis of the Fe-phosphatesmayprovide new insights into ancient habitable environments on Mars.