Geophysical Research Letters

Determination of iron metal optical constants: Implications for ultraviolet, visible, and near-infrared remote sensing of airless bodies



[1] Iron metal is an opaque phase common in planetary materials both as an igneous mineral and as a space-weathering by-product. In either form, iron metal has a large influence on the interpretation of ultraviolet, visible, and near-infrared spectra of planetary surfaces obtained from Earth- or space-based observatories. Therefore, the optical properties of iron are a critical input necessary for accurate theoretical radiative-transfer mixing models for inversion of maturity and mineral proportions from reflectance spectra. Here we report new measurements of the optical constants of iron in the ultraviolet, visible, and near-infrared portions of the electromagnetic spectrum (∼160 to 1700 nm). These values are determined from an iron metal film vapor-deposited onto a fused silica prism. Optical constant determination is carried out using an ellipsometer that performs the measurement within the prism, sensing the side of the metal film unexposed to the ambient atmosphere. The data we report have important implications for modeling planetary spectra and for comparison of laboratory measurements of extraterrestrial samples with remotely sensed data sets.