[论文解读] Scattering and sputtering on the lunar surface; Insights from negative ions observed at the surface

Romain Canu-Blot, Martin Wieser+7 more|arXiv (Cornell University)|Feb 18, 2026

Planetary Science and Exploration被引用 0

一句话总结

本文提出一个半解析模型，用于描述太阳风粒子从月球风化层的散射和溅射，受嫦娥-6 NILS 数据约束，并揭示负氢离子发射的洞见。

ABSTRACT

Context. Airless planetary bodies are directly exposed to solar wind ions, which can scatter or become implanted upon impact with the regolith-covered surface, while also sputtering surface atoms. Aims. We construct a semi-analytical model for the scattering of ions of hundreds of eV and the sputtering of surface atoms, both resulting in the emission of negative ions from the lunar surface. Our model contains a novel description of the scattering process that is physics-based and constrained by observations. Methods. We use data from the Negative Ions at the Lunar Surface (NILS) instrument on the Chang'e-6 lander to update prior knowledge of ion scattering and sputtering from lunar regolith through Bayesian inference. Results. Our model shows good agreement with the NILS data. A precipitating solar wind proton has roughly a 22% chance of scattering from the lunar surface in any charge state, and about an 8% chance of sputtering a surface hydrogen atom. The resulting ratio of scattered to sputtered hydrogen flux is eta_sc / eta_sp = 1.5 for a proton speed of 300 km/s. We find a high probability (7-20%) that a hydrogen atom leaves the surface negatively charged. The angular emission distributions at near-grazing angles for both scattered and sputtered fluxes are controlled by surface roughness. Our model also indicates significant inelastic energy losses for hydrogen interacting with the regolith, suggesting a longer effective path length than previously assumed. Finally, we estimate a surface binding energy of 5.5 eV, consistent with the observations. Conclusions. Our model describes the scattering and sputtering of particles of any charge state from any homogeneous, multi-species surface. Using NILS data, we successfully applied the model to update our understanding of solar wind interacting with lunar regolith, and the emission of negative hydrogen ions.

研究动机与目标

• Develop a physics-based semi-analytical model for scattering and sputtering of hundreds-of-eV particles from lunar regolith capable of emitting negative ions.
• Constrain the model parameters using in situ measurements from the NILS instrument on Chang’e-6.
• Quantify yields, energy and angular distributions, and charge-state probabilities for hydrogen emission.
• Infer surface properties (e.g., binding energy) and energy loss mechanisms from observed negative ion fluxes.

提出的方法

• Define differential number flux J(E,Ω) as a product of total flux, energy distribution J_E, and angular distribution J_Ω.
• Decompose J into scattered and sputtered components and apply charge-state probabilities P^q to obtain J^q.
• Model negative ionization probability P^- using velocity-dependent expressions appropriate for insulating regolith surfaces.
• Map macroscopic emission angles to microscopic emission angles using a regression from Szabo et al. (2022).
• Describe sputtering energy distribution via an extended Ono et al. (2005) framework accounting for elastic and inelastic losses and multi-species regolith (P→S and P→H interactions).
• Compute PKA (primary knock-on atom) densities and energy transfer using extended Kenmotsu-type sputtering theory, including backscattering and energy loss factors.]
• model_idiom_placeholder

Figure 1 : Differential number flux of negative hydrogen ions, $\mathcal{J}^{-}_{\mathrm{H}}$ , versus emission energy. Vertical bars show flux estimates, with thick and thin bars representing the 68% and 90% highest density intervals, respectively. Bar colour qualitatively reflects the signal signi

实验结果

研究问题

• RQ1 What are the scattering and sputtering yields for solar wind protons interacting with lunar regolith at hundreds of eV to keV energies?
• RQ2 What is the probability for emitted hydrogen to appear as a negative ion after surface interaction, and how does it depend on energy and surface properties?
• RQ3 How do energy losses and multi-species surface composition affect the energy/angle distributions of scattered and sputtered hydrogen?
• RQ4 Can NILS surface measurements constrain a unified model of surface-emitted negative ions and their angular/energy profiles?
• RQ5 What surface parameters (e.g., binding energy) are consistent with the observed negative hydrogen fluxes?

主要发现

• About 22% of precipitating protons scatter from the lunar surface in any charge state.
• About 8% of incident protons sputter a surface hydrogen atom.
• The modeled ratio of scattered to sputtered hydrogen flux is 1.5^{+1.5}_{-1.1} at 300 km/s.
• There is a high probability (7–20%) that a hydrogen atom leaves the surface negatively charged.
• Near-grazing emission angles dominate for both scattered and sputtered fluxes, controlled by surface roughness.
• The model implies significant inelastic energy losses for hydrogen, suggesting a longer effective path length in the regolith, and yields a surface binding energy around 5.5 eV.

Figure 2 : Illustration of the solar wind impinging angles (orange) and emission angles (blue). An arbitrary angular emission profile is drawn, with dashed arrows representing possible emission directions. Both the Solar Zenith Angle (SZA) and the emission polar angle $\beta$ are defined relative to