| Institution(s) supplémentaire(s) | Institut d’Astrophysique Spatial, CNRS/Université Paris Sud,France. Aurora Technology B.V., European Space Astronomy Centre/ESA, Madrid, Spain. LESIA, Observatoire de Paris, Université PSL, CNRS |
Abstract | MESSENGER mission to Mercury led to the discovery of hollows. These geological landforms have no close counterpart on other airless silicate bodies. Hollow mostly occur (84.5%) within impact craters and their proximal ejecta while they are rarely found (7%) in high-reflectance red plains (HRP) (Thomas et al., 2014). Their texture and geological setting are suggestive of formation via destruction of a volatile-bearing phase through space weathering processes or sublimation by heating on contact with, or in proximity to, impact melt or volcanic materials (Blewett et al., 2013). Multispectral images and geochemical measurements suggest that hollows are formed by the loss of sulfur-bearing minerals such as CaS or MgS (Vilas et al., 2016). Reflectance spectra of hollows obtained by the Visible and Infrared Spectrograph (VIRS), component of the Mercury Atmospheric and Surface Spectrometer (MASCS) lack absorption features (Barraud et al., 2020). However, MASCS/VIRS spectra show a strong concave curvature between 300 and 600 nm, unique to hollows material (Barraud et al., 2020).
In this work, we present a comparison between reflectance spectra of hollows at high spectral resolution and laboratory spectra of Mercury’s analogs: sulfides, silicates and graphite. Our main objectives are, first, to bring new constraints on the mineral phases and volatile species associated with hollows and then, to further constrain the possibility that hollows are associated with some geochemical and/or spectral units. The best candidates to reproduce the curvature of the hollows’ spectra are CaS, MgS and Na2S. We conduct further work using spectral modelling to quantify the sulfide concentrations in hollows. Our results show that the concentration of sulfides in hollows material is up to two times higher than the sulfides’ concentration derived from chemical measurements in Mercury’s HRP. This study brings for the first time a spectral and compositional argument for the lack of hollows in the HRP of Mercury.
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