Broadband spectrometry and thermal radiative properties of lunar dust simulants

Abstract

Spectrometry of lunar dust simulants can provide better understanding of the Moon’s surface albedo, thermal radiation to its environment, detection of composition variations, and identifying presence of water. The Moon’s soil or regolith is composed of fine dust particles of mostly silica, alumina, and lime, with variations between lighter Highlands (Artemis) regions and darker Mares (Apollo) valleys. To better understand the variations on optical properties, we perform broadband diffuse and specular spectrometry from visible to far-infrared wavelengths of four Lunar regolith simulants. Dust simulants of coarse and fine blends were imaged in scanning electron microscope to validate the particle size distributions. In the visible to near-IR, fine-particle simulants show fewer differences in solar absorption and albedo, while FTIR measurements show compositional oxide differences. Surface absorptivity can vary between 0.63 at the Highlands and 0.79 in Mares, while Lunar albedo obtained from specular spectrometry relative to a Lambertian white reflecting standard can range between 0.79 and 0.64, respectively. Using diffuse FTIR spectrometry, thermal emissivity relative to room temperature blackbody across all Lunar simulants are around 0.78. Variations in spectral reflectance and emittance are dependent on sample humidity and heat treatments, aggregate packing, and scattering from large particles. This work can improve optical sensing methods, dust processing, and in situ resource manufacturing of Lunar regolith.