Synthetic analogs for lava flows on the surface of Mercury: A mid-infrared study

Morlok, Andreas; Sehlke, Alexander; Stojic, Aleksandra N.; Whittington, Alan; Weber, Iris; Reitze, Maximilian P.; Hiesinger, Harald; Helbert, Joern

Abstract

We studied a series of hermean lava analogs in the mid-infrared (2.5 μm–18 μm) to provide characteristic spectra for enstatite basalt, the Northern Volcanic Plains and Na-rich Northern Volcanic Plains. Our aim is to provide spectra for the interpretation of the data expected from Mercury from the MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer) instrument on the ESA/JAXA BepiColombo mission. Bulk powder spectra show bands of glass with a dominating broad Si-O-Si stretching feature around 10 μm. Crystalline components are mainly enstatite and forsterite with Reststrahlen Bands (RBs) around 9.3 μm, 9.6–9.9 μm, 10.0 μm, and 10.3–10.7 μm. Increasing intensity of crystalline features in the spectra reflect the increase in the crystallites in glass with decreasing temperature of equilibration and quenching. Micro-FTIR data allowed to extract spectral of individual components and glass. The position of the Christiansen Feature (CF) has only a weak correlation with the degree of crystallinity. Correlations are observed between the Christiansen Feature (CF) and the bulk SiO2 content of the materials, as does the correlation of this feature with the compositional index SCFM = SiO2/(SiO2 + CaO + FeO + MgO) on an atomic basis. This study also confirms the correlation line of glass-rich, irradiated Mercury analogs in these systems (Weber et al.,2023), indicating a similar spectral response of the glass rich materials expected for the surface of Mercury. The position of the strongest silicate main band (MB) compared to the SiO2 content, confirms a trend for samples formed in experiments simulating high velocity impacts fall on a different trend line than analog samples formed in magmatic processes. A comparison of the results to an Earth-based hermean surface spectrum showed similarities to spectra obtained for NVP samples.