Principal Component Analysis applied on MASCS/MESSENGER data for the spectral investigation of Mercury's surface

The surface of Mercury hosts several spectral units with variations in reflectance and spectral slope, mainly identified after the application of Principal Component Analysis (PCA) on MDIS data, the camera onboard the MESSENGER spacecraft. The major terrains identified on Mercury include the smooth plains such as High -reflectance Red Plains (HRP), Intermediate Plains (IP) and Low-reflectance Blue Plains (LBP), the spectrally Intermediate Terrains (IT) and Low-Reflectance Material (LRM). The minor terrains involve hollows, fresh ejecta, faculae and red material connected to impact craters.This work aims to examine the surface of Mercury by applying the PCA on photometrically corrected and quality-filtered spectra acquired by the MASCS-MESSENGER spectrometer.By combining PC1, PC2 and PC3 components in the red-green-blue image, major terrains (HRP, IP/IT, LBP, LRM) can be distinguished from each other; similarly, among the minor terrains, fresh ejecta and hollows are spectrally distinct from the faculae (connected to volcanism) and red material (related to impact craters). Furthermore, the composite image allows discrimination of the faculae with a spectrally distinct deposit from those with a faint spectral contrast. Examination of PC1 and PC2 separates the surface of Mercury into three sections, characterized by a progressive reddening of the Visible (VIS) spectral slope. Section A includes "spectrally blue" units (LRM, LBP, hollows and fresh ejecta) with lower VIS slope values, whereas Section B involves the "spectrally red" units (RM, HRP, faculae and IT) with higher VIS slope values and with an origin connected to volcanism. The variation in VIS slope could be ascribed to differences in composition or space weathering alterations. Section C, with intermediate PC2 and VIS Slope values, includes terrains with variations in reflectance and spectral slopes. Furthermore, Section C brings to the attention areas distributed around the cold poles longitudes and high latitudes in the southern hemisphere with the maximum surface temperature spanning from 450 K to 650 K. Finally, localized regions corresponding to the walls of craters and explosive vents are also revealed from the Section C, suggesting possible exposure of material slightly altered by solar ion irradiation and/or thermal effects.