Towards quantitative Low Energy Ion Scattering on CaSiO3_3 from Comparison to Multiple-Scattering-Resolved Dynamical Binary Collision Approximation Simulations

We perform Low Energy Ion Scattering with 1\,keV He ions on CaSiO$_3$ using a commercial electrostatic detector system and determine the charge fraction of scattered ions from comparison with Binary Collision Approximation simulations. The simulations take dynamical surface changes due to surface cleaning Ar sputtering into account and scattered He particles are separated into single, dual, and multiple scattering trajectories. We find that the charge fraction of single and dual scattered He is about 10 times higher than the one for multiple collisions. Our results show that quantitative concentration profiles can be inferred from this method, if the charge fraction components are determined first

Creation of Lunar and Hermean analogue mineral powder samples for solar wind irradiation experiments and mid-infrared spectra analysis

The surfaces of airless planetary bodies are subject to a barrage of charged particles, photons, and meteoroids. This high-energy space environment alters the surfaces and creates a tenuous atmosphere of ejected particles surrounding the celestial bodies. Experiments with well characterized analogue materials under controlled laboratory conditions are needed to interpret the observations of these atmospheres and improve composition models of such bodies. This study presents methods to create and analyze mineral powder pellets for ion irradiation experiments relevant for rocky planetary bodies including the Moon and Mercury. These include the pyroxenes diopside and enstatite, the plagioclase labradorite and the non-analogue pyroxenoid wollastonite. First ion irradiation experiments with diopside, enstatite and wollastonite pellets were performed under UHV with 4 keV He+ at fluences of several 1021 ions m−2 (~100 and ~1000 years for Mercury and the Moon, respectively). The pellet's thermal IR reflectance properties were compared before and after irradiation showing monotonously shifting IR spectral features between 7 − 14 μm towards higher wavelengths. For all irradiated pellets, Reststrahlen bands shifted by ~0.03 μm. Surface abrasion was found to remove the sputter effect, which is restricted to the top few tens of nm of the surface. Additionally, ion irradiation experiments were performed in a quartz crystal microbalance catcher setup, where the mass sputtered from pellets was monitored. This proves, that the presented sample preparation method allows the study of irradiation induced sputtering and surface alteration on the surfaces of rocky planets under laboratory conditions

New Compound and Hybrid Binding Energy Sputter Model for Modeling Purposes in Agreement with Experimental Data

Rocky planets and moons experiencing solar wind sputtering are continuously supplying their enveloping exosphere with ejected neutral atoms. To understand the quantity and properties of the ejecta, well-established binary collision approximation Monte Carlo codes like TRIM with default settings are used predominantly. Improved models such as SDTrimSP have come forward, and together with new experimental data, the underlying assumptions have been challenged. We introduce a hybrid model, combining the previous surface binding approach with a new bulk binding model akin to Hofsäss & Stegmaier. In addition, we expand the model implementation by distinguishing between free and bound components sourced from mineral compounds such as oxides or sulfides. The use of oxides and sulfides also enables the correct setting of the mass densities of minerals, which was previously limited to the manual setting of individual atomic densities of elements. All of the energies and densities used are thereby based on tabulated data, so that only minimal user input and no fitting of parameters are required. We found unprecedented agreement between the newly implemented hybrid model and previously published sputter yields for incidence angles up to 45° from surface normal. Good agreement is found for the angular distribution of mass sputtered from enstatite MgSiO _3 compared to the latest experimental data. Energy distributions recreate trends of experimental data of oxidized metals. Similar trends are to be expected from future mineral experimental data. The model thus serves its purpose of widespread applicability and ease of use for modelers of rocky body exospheres