¹Qinting Jiang,¹Shun-ichiro Karato,^2,3Thilo Bissbort,³Varvara Foteinou
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2024.115958]
¹Department of Earth and Planetary Science, Yale University, 210 Whitney Avenue, New Haven, CT 06520, USA
²Department of Earth and Environmental Sciences, Ludwig-Maximilians-University, Theresienstr. 41, 80333 Munich, Germany
³Central Unit for Ionbeams and Radionuclides RUBION, Ruhr-University Bochum, Universitätsstraße 150, 44801 Bochum, Germany
Copyright Elsevier

The solar wind is a possible source for hydrogen and other volatiles on planetary bodies. To better understand the role of the solar wind during the volatile acquisition of planetary materials, we conducted hydrogen implantation experiments on olivine, orthopyroxene, quartz single crystals. Depth profiles of hydrogen concentration after implantation are determined by the Nuclear Resonance Reaction Analysis. We find that energetic hydrogen particles penetrate into the sample and accumulate at a certain depth. The hydrogen concentration increases with the hydrogen fluence until a “saturation level” is attained. Hydrogen saturation level (e.g., ~10–20 at.% in olivine, equivalent to 0.5–1.2 wt%) far exceeds the equilibrium solubility in the bulk crystal at a similar thermodynamic condition (~10−22 wt%). The results of olivine show that the hydrogen penetration depth increases whereas the saturation level decreases (weakly) with the beam energy. Hydrogen saturation level also depends on the mineral species in the order: olivine > orthopyroxene > quartz. The experimental results can be applied to explain some observations on the high surface water content of some planetary bodies including Itokawa asteroid and the Moon. We also explore the possibility of hydrogenated dusts by the solar wind implantation as a source for water on terrestrial planets. We conclude that if all dusts were exposed to the solar wind and all implanted hydrogen were converted to water, then >10 ocean masses would have been acquired for Earth by ~100 years. However, the main part of the proto-planetary disk was not exposed to the solar wind and dusts could have been hydrogenated only when they were far from the equatorial plane of the disk. We discuss a possible mechanism to transport the hydrogenated dusts to the disk interior via turbulent mixing. Also, our experimental results and the mass dependence of the particle energies in the solar wind suggest that the D/H ratio of the dusts exposed to the solar wind will be higher than the solar wind value.

¹Zaicong Wang et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.01.002]
¹State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Copyright Elsevier

Sulfides are accessory phases in lunar rocks but are important for understanding lunar interior processes as well as impacts on the lunar surface. Whether or not the lunar mantle had achieved sulfide saturation during magma ocean evolution and displays homogeneous sulfur isotopes remains under debate. The Chang’e-5 (CE-5) mission returned young (2.0 Ga) basalts from a mare terrain in the northern Oceanus Procellarum. Here we study chemical and sulfur isotopic compositions (δ34SV-CDT) of sulfides from CE-5 basaltic fragments and combine them with δ34S of other young (3.1–3.0 Ga) lunar low-Ti basalt (NWA 10597 and NWA 4734) and gabbro meteorites (NWA 6950) to compare them with Apollo low-Ti and high-Ti mare basalts. The sulfides in basaltic fragments of CE-5 are troilites (FeS) with low abundances of Ni, Co, and Cu (e.g., Ni < 0.04 wt.% and Ni/Co < 0.3). Textures and chemical compositions indicate that most troilites are late-stage crystallization products from the highly evolved CE-5 basalts. Several troilites occur in the matrices of impactite clasts and are intergrown with Fe–Ni metal (12–36 wt.% Ni, Ni/Co of 12–39). These troilites are distinct from the major population of troilites with noticeably higher Ni abundances (mostly >0.2 wt.% with Ni/Co of 1–3) and reconcile with the addition of meteoritic materials into the impact melts.

The δ34SV-CDT of large troilite grains (>10 μm) from the CE-5 basaltic fragments and lunar meteorites were obtained by high-precision, high-spatial-resolution femtosecond laser ablation MC-ICP-MS which achieved external uncertainty (0.65‰, 2SD at 8-μm laser spots) like nano-SIMS. Sulfur degassing during surficial effusive lava flow likely led to a slight decrease in δ34S (by ∼1‰) for some basaltic fragments; however, such effects were limited to the scale of bulk rock samples, consistent with previous results. The mean δ34S of troilites in CE-5 basaltic fragments (0.35±0.25‰, 2SE, n = 45) is similar to those of ancient (3.8–3.1 Ga old) Apollo low-Ti and high-Ti mare basalts and the young gabbro cumulate NWA 6950 (0.56 ± 0.21‰, 2SE, n = 10). The paired NWA 10597 and NWA 4734 show consistent δ34S, lower than most values by ∼0.5‰. Current data thus indicate that most mantle sources of lunar basalts would be homogeneous for δ34S (0.6 ± 0.3 ‰) and minor regions may be different. The overall homogenous δ34S from different mantle sources with variably low sulfur content supports sulfide-undersaturated accumulation of the lunar magma ocean, which was inherited from strong volatile loss and evaporative fractionation during the formation of the Moon.