Mercury: Absence of crystalline Fe 2+ in the regolith

Abstract

Reflectance spectra of terrain on Mercury containing both smooth plains and intercrater plains were obtained using a charge-coupled device spectrograph on 24 November 1984. The composite spectrum covers the 0.53- to 1.02-μm spectral range with a resolution of 17 Å. Absorption features due to telluric H 2O absorption are clearly mapped around 0.73, 0.82, and 0.93 μm. No evidence exists in the new spectrum for the proposed orthopyroxene absorption centered near 0.9 μm seen in older spectra of this terrain. The surface material is probably highly reduced, with any iron present in metallic form. Based upon the new spectrum, a history of heavy micrometeoroid bombardment of the Mercurian surface is suggested, resulting in a surface regolith primarily comprised of agglutinates.