Simulated Solar-wind-induced Space Weathering of Olivine Powders: Spectral Alterations in the Ultraviolet, Visible, and Near-infrared

Abstract

Bombardment by solar wind ions is one of the main drivers of space weathering on airless bodies. Here, we simulate the solar-wind-driven spectral alteration of loosely packed olivine powders by irradiation with 1.2 keV helium ions (He ^+ ). We measured the reflectance spectra of the olivine powder in the ultraviolet–visible–near-infrared (UV–Vis–NIR) wavelength range (0.2–2 μ m) as a function of ion fluence. In the Vis–NIR range, we observed spectral darkening, absorption band shallowing, and spectral reddening, in agreement with lunar-style space weathering and previous laboratory studies. In the UV–Vis, spectral darkening was also observed. However, a spectral bluing took place at wavelengths below 400 nm. As the simulated space weathering progressed, the spectral slopes shifted from steep-UV/shallow-NIR slopes to shallow-UV/steep-NIR slopes. Moreover, the change in the UV slope was almost 10 times larger than in the NIR, supporting the hypothesis that the UV spectral slope could be an earlier indicator of space weathering.

Keywords

• Asteroid surfaces
• Solar wind
• Infrared spectroscopy
• Ultraviolet spectroscopy
• Planetary science
• Experimental techniques