Comparison of space weathering spectral changes induced by solar wind and micrometeoroid impacts using ion- and femtosecond-laser-irradiated olivine and pyroxene

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 1018 particles 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.

Sub-surface alteration and related change in reflectance spectra of space-weathered materials

“…We used samples identical to those in Chrbolková et al (2021), that is pellets made of a pressed powder (with particle sizes < 106 µm) of olivine (forsterite number Fo90), further denoted as OL, and pyroxene (enstatite number En67), further denoted as OPX, on top of a KBr base. We refer the reader to Chrbolková et al (2021) for more details.…”

“…For the microscopical observations, we used four different irradiated pellets from Chrbolková et al (2021). Two of them were produced by H + irradiation, and the other two by femtosecond laser irradiation.…”

“…The effect of the solar wind is usually simulated by irradiation of the samples by various ions (see, for example, the work of Brunetto et al 2014, Demyk et al 2001, Hapke et al 1970, or Loeffler et al 2009 for more details). The effect of micrometeoroid impacts is mainly studied using individual or repeated laser pulses of various durations and energies (see, for example, Sasaki et al 2001, Sasaki et al 2002, and Yamada et al 1999 for usage of nanosecond laser pulses or Fazio et al 2018 andChrbolková et al 2021 for femtosecond laser pulses). Only rarely do experiments include actual impacts of dust particles, such as in Fiege et al (2019).…”

“…This article is a follow-up of Chrbolková et al (2021), where we evaluated the difference in the spectra influenced by solarwind irradiation and micrometeoroid bombardment. This was done through laboratory irradiations of olivine and pyroxene pellets using low-energy 5 keV H + ions and individual femtosecond laser pulses as in Fazio et al (2018).…”

“…In Chrbolková et al (2021), we only evaluated the spectral change, but we did not have information on the material changes within the pellets. In this article, we aim to find the connection between the spectral changes and the sub-surface alteration caused by the different space weathering agents.…”