Abstract
Context.Space weathering is a process that changes the surface of airless planetary bodies. Prime space weathering agents are solar wind irradiation and micrometeoroid bombardment. These processes alter planetary reflectance spectra and often modify their compositional diagnostic features.Aims.In this work we focused on simulating and comparing the spectral changes caused by solar wind irradiation and by micrometeoroid bombardment to gain a better understanding of these individual space weathering processes.Methods.We used olivine and pyroxene pellets as proxies for planetary materials. To simulate solar wind irradiation we used hydrogen, helium, and argon ions with energies from 5 to 40 keV and fluences of up to 1018particles cm−2. To simulate micrometeoroid bombardment we used individual femtosecond laser pulses. We analysed the corresponding evolution of different spectral parameters, which we determined by applying the Modified Gaussian Model, and we also conducted principal component analysis.Results.The original mineralogy of the surface influences the spectral evolution more than the weathering agent, as seen from the diverse evolution of the spectral slope of olivine and pyroxene upon irradiation. The spectral slope changes seen in olivine are consistent with observations of A-type asteroids, while the moderate to no slope changes observed in pyroxene are consistent with asteroid (4) Vesta. We also observed some differences in the spectral effects induced by the two weathering agents. Ions simulating solar wind have a smaller influence on longer wavelengths of the spectra than laser irradiation simulating micrometeoroid impacts. This is most likely due to the different penetration depths of ions and laser pulses. Our results suggest that in some instances it might be possible to distinguish between the contributions of the two agents on a weathered surface.
Highlights
The surfaces of airless planetary bodies in the solar system are permanently exposed to the space environment, which consists mainly of solar wind irradiation and micrometeoroid bombardment
In this work we focused on simulating and comparing the spectral changes caused by solar wind irradiation and by micrometeoroid bombardment to gain a better understanding of these individual space weathering processes
We fitted all of the measured spectra using the Modified Gaussian Model (MGM), as described in Sect. 2.4, and plotted the spectral parameters as a function of astrophysical timescale, which we calculated from irradiation fluences and crater densities in accordance with the solar wind and dust fluxes at 1 au
Summary
The surfaces of airless planetary bodies in the solar system are permanently exposed to the space environment, which consists mainly of solar wind irradiation and micrometeoroid bombardment. These processes cause changes to the topmost surface layers of the bodies, resulting in an alteration of their spectroscopic features (Hapke 1965, 2001; Wehner et al 1963). Among the most prominent visible (VIS) and near-infrared (NIR) spectral changes observed on dry silicate bodies, such as the Moon or S-type asteroids, are spectral slope reddening (a decrease in reflectance towards shorter wavelengths), reduction of the diagnostic 1 and 2 μm absorption bands (Burns 1989), and an overall darkening of spectra The most prominent MIR changes are the alteration of the shape, position, and relative intensities of
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