Fe-phosphates in Jezero Crater as evidence for an ancient habitable environment on Mars
T. V. Kizovski, Mark Schmidt, L. P. O’Neil, Michael W. Jones, Nicholas J. Tosca, David A. K. Pedersen, J. A. Hurowitz, C. T. Adcock, Elisabeth M. Hausrath, K. L. Siebach, U. Wolf, Sunanda Sharma, S. J. VanBommel, F. M. McCubbin, E. A. Cloutis, Morgan L. Cable, Yang Liu, B. C. Clark, A. H. Treiman, Michael M. Tice, David C. Catling, J. N. Maki, Tanja Bosak, B. P. Weiss, Alberto González Fairén, John R. Christian, Abigail L. Knight, Andrew O. Shumway, Nicolas Randazzo, Peter S. Jørgensen, Peter R. Lawson, Lawrence A. Wade, Christopher M. Heirwegh, W. T. Elam, Abigail C. Allwood
Abstract
Phosphorus is an essential component for life, and in-situ identification of phosphate minerals that formed in aqueous conditions directly contributes toward one of the main goals of the Mars 2020 Perseverance rover: to seek signs of ancient habitable environments. In Jezero crater, proximity science analyses within a conglomerate outcrop, “Onahu” demonstrate the presence of rare Fe3+-bearing phosphate minerals (likely metavivianite, ferrolaueite, (ferro)beraunite, and/or santabarbaraite) embedded in a carbonate-rich matrix. While Fe-phosphates have been inferred previously on Mars, this work presents the most definitive in-situ identification of martian Fe-phosphate minerals to date, using textural, chemical, spectral, and diffraction analyses of discrete green-blue grains. The Fe-phosphate minerals’ textural context along with comparisons to Earth analogs suggest they likely formed after oxidation of Fe2+-phosphate vivianite, the most common Fe-phosphate in sedimentary environments on Earth, often associated with microbial activity and organics. While there is no obvious evidence of biological inputs in Onahu, if the Fe-phosphates’ formation environment was similar to vivianite-rich sedimentary environments on Earth, these minerals likely originally precipitated in conditions favorable to potential martian life — in a low temperature, reducing aqueous medium with high concentrations of bio-limiting elements, and Fe-redox gradients that could provide an energy source. If the sample collected from Onahu (Otis_Peak) is returned to Earth, analysis of the Fe-phosphates may provide new insights into ancient habitable environments on Mars. The Perseverance rover has made the most definitive identification of Fe-phosphate minerals on Mars to date. High-resolution chemical and textural PIXL analyses suggest they originally formed after vivianite in a potentially habitable environment.