Characterizing Potential Rock Coatings at the Perseverance Rover Landing Site: A Multispectral Analysis with Mastcam-Z

The NASA Mars 2020 Perseverance rover is currently exploring an ancient lacustrine environment at Jezero crater to investigate regional geology, evaluate past habitability, seek signs of ancient life, and cache samples for future return. The Mastcam-Z instrument, a pair of zoomable multispectral cameras on the Perseverance rover, has acquired images of the landing site on the crater floor to help characterize morphologic, textural, sedimentological, and multispectral properties of the surrounding rock units. These images have revealed rocks with various textural and morphologic expressions that suggest differences in erosional history and potentially lithology. Purple-hued patches have been commonly observed by the Mastcam-Z instrument on surfaces of various rock types surrounding the landing site. Here we characterize the morphologic and multispectral properties of these purple surface expressions to constrain the origin and investigate potential alteration history of the landing site rocks. The purple patches are typically observed in less dusty areas of most rock surfaces, especially those laser-ablated by SuperCam LIBS activities. The purple areas are particularly apparent in Mastcam-Z decorrelation stretch images, which are processed using principal components analysis to exaggerate color differences. Multiple manifestations of these purple surfaces have been observed, including as patches with raised edges on wind-abraded surfaces, clast-shaped patches similar in size to surrounding holes within the rock, or larger dust-free surfaces that appear to represent the body of the rock. These different expressions suggest the purple patches may represent clasts or infillings, the remnants of a surface coating, or alteration of the rock matrix. Mastcam-Z multispectral data in the visible/near-infrared (VNIR; 440-1100nm) indicate these purple areas commonly display a narrow absorption band near 860 nm, possibly consistent with both fine-grained crystalline hematite and poorly crystalline iron oxides.