Revealing the loss of sulfur on troilite under simulated solar wind H+ irradiation

The depletion of sulfur in space-weathered sulfides (e.g., troilite) has been observed on the Moon and asteroids. However, the loss process, loss rate, and modification mechanism of sulfur in troilite under space-weathering conditions remain unclear. In this study, 1.5 keV H^{+ ions with a fluence of (1.0 ± 0.1) × 1018 ions/cm2 were used to irradiate troilite to simulate the space-weathering process on the Moon. The results show that the H+ ion irradiation not only forms dome-like microstructures on the surface of troilite crystal, but also generates an irradiated layer of ~80 nm on its surface. In this irradiated layer, a loss of sulfur (S content < 5 wt%) is clearly observed compared with that in the unirradiated troilite (S content = 37 wt%). Crystallographically, the irradiated troilite transformed from a single-crystalline to a polycrystalline state. This work, for the first time, reveals the microstructural alteration characteristics of space-weathered troilite through simulation experiments. We have quantitatively constrained the sulfur mass loss rate of troilite to 0.1 wt%/yr on the Moon. Furthermore, this study provides critical experimental evidence of the modification of volatiles (e.g., sulfur) on the airless planetary surfaces due to space weathering.}