The big lobe of 67P/Churyumov–Gerasimenko comet: morphological and spectrophotometric evidences of layering as from OSIRIS data

Between 2014 and 2016, ESA’s Rosetta OSIRIScameras acquired multiple-filters images of the layered nucleus of comet 67P/Churyumov–Gerasimenko, ranging from ultraviolet to near-infrared wavelengths. No correlation between layers disposition and surface spectral variegationhas been observed so far. This paper investigates possible spectral differences among decametre-thickness outcroppinglayers of the biggest lobe of the comet by means of OSIRISimage dataset. A two-classes maximum likelihood classification was applied on consolidated outcropsand relative deposits identified on post-perihelion multispectral imagesof the big lobe. We distinguished multispectral data on the basis of the structural elevation of the onion-shell Ellipsoidal Model of 67P. The spatial distribution of the two classes displays a clear dependence on the structural elevation, with the innermost class resulting over 50 per cent brighter than the outermost one. Consolidated cometarymaterials located at different structural levels are characterized by different brightness and revealed due to the selective removal of large volumes. This variegationcan be attributed to a different texture of the outcropsurface and/or to a different content of refractory materials.