Investigating VNIR spectral properties of Mercury, what we can learn about composition from remote sensing and laboratory analogues

The MESSENGER mission provides new constrains on the Mercury surface and its geological history. In particular, we have knowledge of peculiar geological features and new insight of the reflectance spectral properties in the VNIR, and lower spatial scales elementary composition. The volcanic material on Mercury shows, in general, low Fe/Si (i.e., < 1wt.% FeO) and variable Al/Si, Mg/Si and Ca/Si ratios; moreover, K/Si, Na/Si and K/Th ratios are higher than expected. The abundance of S and C is unexpected high, suggesting an anomalous large contribution of volatiles, which correlates with the presence of large pyroclastic deposits, hollows which are features associated to degassing, and dark, blue terrains (e.g., Rothery et al., 2020). Reflectance highlights the heterogeneity of the surface, showing a large spectral variety among the terrains and, in particular, pyroclastic deposits, hollows and potential C-rich regions with specific spectral characteristics that permit to differentiate them. In this work, we studied the spectral properties from MDIS camera color filters mosaics of the Kuiper quadrangles, recently studied from a geological point of view by Giacomini et al. (2021). We investigate the Kuiper quadrangle at different spatial resolution (and coverage) to show the relationship between the different geological units and to obtain the spectral characteristics of local features at the highest possible resolution. In particular, we show how spectral properties similar to the hollows in Dominici Crater (see Rothery et al., 2020 and reference therein) are present in different bright features, either recognized as hollows or not. Hollows show some spectral properties that seems to be different from other geological features, although some small secondary fresh craters looks like spectrally similar to those features. Another interesting aspect of this quadrangle is the presence of different craters with pyroclastic deposits and vents, some of which are associated with hollows. Pyroclastic deposits and vents appear similar (with the vents that are often brighter), but distinct from the hollows. Moreover, spectral properties within some vents indicate similarities with the hollows (e.g., Mistral Crater),which however do not have morphological counterparts. Finally, here we discuss also the spectral characteristics of potential analogues from the compositional or spectral point of view, as iron pure achondrites (i.e., aubrites), Mercury-like analogues glasses, and mineral mixtures of igneous rocks with graphite or sulphides. Our aim is extrapolate indication that could help in mineralogical interpretation from MESSENGER data and, in particular, the future BepiColombo measurements.