From Earth to Mercury: Compositional, Reflectance Spectroscopy, and Emissivity Studies on Boninites as Surface Natural Analogs

Kurzfassung

Boninites are high-magnesium volcanic rocks proposed as terrestrial analogs for Mercury's surface, based on elemental data from NASA's MErcury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) mission. In this study, we investigated boninite samples from the Troodos Massif (Cyprus) using a multi-methodological approach to characterize their mineralogical, chemical, and spectroscopic properties, including reflectance and emissivity spectra. Geochemical analyses confirm that the bulk composition of the samples closely matches Mercury's geochemical terrains in terms of SiO2, MgO, and Al2O3 content, though FeO concentrations are higher (∼8 wt% vs. 1–2 wt%). Samples from different localities show some mineralogical differences but generally contain less orthopyroxene and albitic plagioclase than expected on Mercury, along with hydrated minerals from aqueous alteration, which are not expected on the planet's surface. Reflectance spectra in the ultraviolet (UV), visible (VIS), and near-infrared (NIR) range show major absorption features around 1 μm, associated with mafic minerals, and minor bands at ∼1.4 μm, ∼1.9 μm, and 2.2–2.3 μm, linked to hydrated phases, with spectral variations reflecting mineralogical differences. In the mid-infrared (MIR) range and emissivity spectra, we observe Christiansen Features (CF) and Reststrahlen Bands (RB) at different positions, mainly influenced by plagioclase content, and shifts in emissivity minima with increasing temperature. Spectral differences between the boninites and Mercury mainly result from the intrinsic mineralogy of the samples. Nonetheless, Troodos boninites represent one of the best Mercury analogs currently available on Earth, and understanding their spectral behavior in relation to their mineralogy could support future investigations with the ESA/JAXA BepiColombo mission.