Space Weathering Effects in Troilite by Simulated Solar‐Wind Hydrogen and Helium Ion Irradiation

Abstract

Space weathering is a key process in the interpretation of airless planetary surfaces. As we engage new missions to planetary objects with potentially novel surfaces such as 16 Psyche, there is renewed interest in expanding our knowledge of space weathering effects to a wider variety of analog materials, including the physical/chemical effects of solar‐wind ions on planetary regoliths. We have experimentally simulated the effects of solar ions on two polished thick sections of meteoritic troilite (FeS) via irradiation with 1 keV hydrogen (H+) and 4 keV helium (He+), to investigate effects resulting from different ion species. We detected depletion of sulfur over the course of each irradiation using in situ X‐ray photoelectron spectroscopy. Sulfur depletion rates were surprisingly similar for H+ and He+, interpreted as a function of subsurface ion‐activated diffusion. By comparing XPS‐derived elemental abundances with SDTrimSP computer simulations, we further quantified sulfur diffusion, sputtering yield, and altered‐layer composition with respect to incident‐ion fluence, and accounted for the influence of surface oxidation due to atmospheric sample storage. Using scanning electron microscopy, we detected an increase in nanoscale surface roughness resulting from the irradiation, which we quantified using atomic force microscopy. Based on these results, we estimate that an exposure time of order 103 Earth‐years is required for troilite on Psyche to reach equilibrium sulfur depletion within the first atomic layer.

Deducing Lunar Regolith Porosity From Energetic Neutral Atom Emission

“…SDTrimSP‐3D represents a three‐dimensional expansion of SDTrimSP and allows the implementation of a surface morphology or more complex structures on a grid of cuboid voxels. SDTrimSP is often used for studying ion‐surface interaction in nuclear fusion research (Oberkofler et al., 2015; Schmitz et al., 2018; Sugiyama et al., 2016), and has also been applied for simulating systems relevant to space weathering to better understand sputtering (Morrissey et al., 2022; Schaible et al., 2017; Szabo, Biber, Jäggi, Brenner, et al., 2020; Szabo, Biber, Jäggi, Wappl, et al., 2020), ion implantation (Biber et al., 2020), or ion‐induced surface composition changes (Christoph et al., 2022). The scattering of ions from surfaces has also been compared to SDTrimSP simulations by Deuzeman (2019), finding a good agreement with experimental data for several cases.…”

Space weathering signatures in sulfide and silicate minerals from asteroid Itokawa

“…In addition, other laboratory simulations of solar wind irradiation of troilite employed X-ray photoelectron microscopy (XPS) to reveal the preferential sputtering of sulfur from the surface of the sulfide during 4 keV He + and Ar + ion irradiation experiments (Loeffler et al 2008 ). Moreover, Christoph et al ( 2022 ) identified sulfur depletion after 1 keV H + and 4 keV He + irradiation of troilite from Canyon Diablo and Toluca meteorites using XPS and performed the collisional simulations on the Static and Dynamic Trim for Sequential and Parallel computer (SDTrimSP) software to identify the physical factors contributing to the sulfur depletion. The simulations show that by adding radiation-enhanced diffusion on the model, the fit between the concentrations of Fe and S obtained from SDTrimSP and the concentrations identified in the XPS data improved significantly.…”

“…The simulations show that by adding radiation-enhanced diffusion on the model, the fit between the concentrations of Fe and S obtained from SDTrimSP and the concentrations identified in the XPS data improved significantly. During radiation-enhanced diffusion, ion irradiation creates defects in the target lattices (i.e., vacancies and interstitials) (Betz and Wehner 1983 ) that promote the diffusion of volatile species towards the surface where they are subsequently sputtered (Christoph et al 2022 ). This suggests that in addition to sputtering, radiation-enhanced diffusion might enhance sulfur loss in sulfides during ion irradiation from the solar wind.…”

Establishing a Best Practice for SDTrimSP Simulations of Solar Wind Ion Sputtering

“…Based on the lack of a significant O reduction in these previous surface concentration measurements for several different silicates,it appears unlikely that the O SBE could be 1 eV. However, it is unknown if a process such has radiation-enhanced diffusion may replenish the sputtered surface O in those experiments, and thus making these low SBEs possible (Quadery et al 2015;Chaves & Thompson 2022;Christoph et al 2022). Here, we consider the 6.5 eV SBE to be the most likely, but for the sake of completeness we include O SBE values of 2.6 subsequent simulations.…”