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Sputter Yields of Lunar Soil Under Solar Wind Ion Impact

Presentation #101.02 in the session Moon & Earth I (Oral Presentation)

Published onOct 23, 2023
Sputter Yields of Lunar Soil Under Solar Wind Ion Impact

One of the influences that the Moon experiences in the space environment is the precipitation of solar wind ions onto its surface. A consequence of this irradiation is the release of surface material through the process of sputtering. The ejected particles subsequently contribute to the formation of the lunar exosphere [1]. Thus, to properly model the exosphere evolution, it is necessary to understand the sputtering of the lunar surface and experimentally constrain relevant quantities like the sputter yield and the angular distribution of the ejecta [2].

For this purpose, we present laboratory studies on the sputtering of lunar regolith acquired during the Apollo 16 mission (#68501) as a complement to the more commonly used analogues or simulants. We followed the approach described in [3]: A thin, vitreous film of regolith material was grown onto a quartz resonator that served as a quartz crystal microbalance (QCM). This technique allowed us to study the mass depletion under He and H ion impact at solar wind energies in situ and in real time. Therefore, we can quantify the sputter yield as a function of incidence angle. Moreover, a second QCM was placed such that it faces the irradiated sample for measuring the mass increase due the sticking of sputtered particles. Rotation of this catcher QCM around the sample allowed us to probe the angular distribution of ejecta.

We repeated these measurements with pellets pressed from the lunar regolith and prepared analogous to the description in [4]. These pellets provide a better representation of the lunar surface because they largely maintain their original grains and roughness. However, sputter yields can only be determined with the catcher QCM. For two incidence angles, this information was inferred by comparison of the angular emission characteristics with the ones obtained from the thin film reference measurements. These experiments thus allow us to probe the sputtering behavior of lunar regolith with unprecedented precision. We will present these experimental findings along with simulation approaches to model these results, providing insights into the sputtering of the surfaces of the Moon and other celestial bodies.

[1] Hapke, B. et al; J. Geophys. Res. 106 (2001): 10039 [2] Wurz, P. et al; Icarus 192 (2007): 486 [3] Biber, H. et al; Planet. Sci. J. 3.12 (2022): 271 [4] Jäggi, N. et al; Icarus 365 (2021): 114492

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