Characterization of compositional endmembers in PIXL scans

The Planetary Instrument for X-ray Lithochemistry (PIXL) onboard the Perseverance rover collects high-resolution geochemical data at hundreds to thousands of individual measurement spots per scan. Here, we develop an unmixing model to retrieve and map compositional endmembers in PIXL scans and apply it to a selection of observations from the first ~1200 sols of the Perseverance mission. From this study we conclude that PIXL can characterize compositional endmembers present at abundances as low as 3–4% by volume or scattered individual grains as small as 20 μm in diameter. In flight scans, this unmixing model extends carbonate detections in an olivine cumulate in the floor of Jezero crater to scattered smaller grains and identifies the presence of a Ca-phosphate endmember in a boulder on the Jezero delta Upper Fan. Incorporation of the presented methodologies into PIXL's standard analytical pipeline will improve the capability to detect and characterize low-abundance minerals in PIXL scans.