Magnetic Susceptibility of Submicroscopic Metallic Iron Formation Through Laser Irradiation of Olivine

Abstract:

Surfaces of exposed solids change their integrity due to solar wind and micrometeorite impacts, resulting in significant modification of exposed mineral grains. Apart from the possibility of in-situ ice generation, initial iron rich composition allows for re-precipitation of iron. The importance of characterizing these SMFe (submicroscopic metallic iron) particles exists to better our interpretations in remote sensing of planetary surface minerals. For example, the presence of SMFe changes the spectral reflectance of silicate minerals in the visible (VIS) to near-infrared (NIR) wavelengths, and contributes to “space weathering”: (1) SMFe darkens the overall reflectance, (2) steepens (or reddens) the spectral slope, and (3) decreases the contrast in the 1 µm band. Irradiating olivine samples with energies simulating micrometeorite impact energies revealed single domain (SD) and superparamagnetic (SPM) iron grains varying in size. All samples exhibit general VIS-NIR space weathering effects, but also magnetic anomalies in the immediate surface proximity and frequency dependent magnetic susceptibility changes due to the production of SMFe. Planetary minerals such as olivine produce more SMFe when micrometeorite impacts and/or solar wind irradiation increases. Magnetic textures found during the scanning of the laser irradiated samples reveal anomalies that are dominantly caused by metallic iron and are in superparamagnetic state while at room temperature. We observed an increased dispersion of these metallic anomalies when irradiation energy increased. Frequency dependent magnetic susceptibility measurements creates a data set that has potential to become a tool in remote detection of these surfaces by deep penetration radar incidence.