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In the absence of a protecting atmosphere, the surfaces of rocky bodies in the solar system are affected by significant space weathering due to the exposure to the solar wind [1]. Fundamental knowledge of space weathering effects, such as optical changes of surfaces as well as the formation of an exosphere is essential for gaining insights into the history of planetary bodies in the solar system [2]. Primarily the exospheres of Mercury and Moon are presently of great interest and the interpretation of their formation processes relies on the understanding of all space weathering effects on mineral surfaces.Sputtering of refractory elements by solar wind ions is one of the most important release processes. We investigate solar wind sputtering by measuring and modelling the sputtering of pyroxene samples as analogues for the surfaces of Mercury and Moon [3, 4]. These measurements with thin film samples on Quartz Crystal Microbalance (QCM) substrates allow recording of sputtering yields in-situ and in real time [5]. For the simulation of kinetic sputtering from the ion-induced collision cascade we use the software SDTrimSP with adapted input parameters that consistently reproduce measured kinetic sputtering yields [4, 6].This study focuses on investigating the potential sputtering of insulating samples by multiply charged ions [7]. Changes of these sputtering yields with fluence are compared to calculations with a model based on inputs from SDTrimSP simulations. This leads to a very good agreement with steady-state sputtering yields under the assumption that only O atoms are sputtered by the potential energy of the ions. The observed decreasing sputtering yields can be explained by a partial O depletion on the surface [4]. Based on these findings expected surface composition changes and sputtering yields under realistic solar wind conditions can be calculated. Our results are in line with previous investigations (see e.g. [8, 9]), creating a consistent view on solar wind sputtering effects from experiments to established modelling efforts. References:[1] B. Hapke, J. Geophys. Res.: Planets, 106, 10039 (2001).[2] P. Wurz, et al., Icarus, 191, 486 (2007).[3] P.S. Szabo, et al., Icarus, 314, 98 (2018).[4] P.S. Szabo, et al., submitted to Astrophys. J. (2020).[5] G. Hayderer, et al., Rev. Sci. Instrum., 70, 3696 (1999).[6] A. Mutzke, et al., “SDTrimSP Version 6.00“, IPP Report, (2019).[7] F. Aumayr, H. Winter, Philos. Trans. R. Soc. A, 362, 77 (2004).[8] H. Hijazi, et al., J. Geophys. Res.: Planets, 122, 1597 (2017).[9] S.T. Alnussirat, et al., Nucl. Instrum. Methods Phys. Res. B, 420, 33 (2018).

Bodies in space without a dense atmosphere are affected by several erosive space weathering processes [1, 2]. These processes are responsible for modifications of surface properties as well as for the formation of an exosphere. During the BepiColombo mission, an on-board mass spectrometer will probe this exosphere on Mercury. Knowledge the different processes causing its formation is crucial for the interpretation of the obtained mass spectrometry data [3, 4]. Sputtering by solar wind ions is expected to be one of the key drivers of the particle release that leads to the formation of the exosphere. In addition, these ions can modify the regolith, become implanted and are released into the exosphere [5, 6].We emulate solar wind precipitating onto the surface of Mercury by irradiating analogue material with mass over charge selective ion sources. For this study in particular, a magnesium rich augite (Ca,Fe)(Mg,Fe)[Si2O6] sample was used as analogue. The material is deposited onto a Quartz Crystal Microbalance (QCM) as thin film. Chemical composition and thickness of these films was investigated by means of ion-beam analysis [7]. The QCM-technique allows for real time measurements of mass changes during the experiments. This approach enables us to determine sputter yields due to ion impact, as well as projectile implantation and rerelease. Furthermore, the target is heatable and desorbed atoms can be analyzed with a quadrupole mass spectrometer. The setup thus allows for Thermal Desorption Spectroscopy (TDS) measurements. Together with the QCM, temperature dependence of the projectile rerelease and the total mass change during heating cycles can be determined.Irradiation of the targets with He+ at solar wind energies of 4keV were performed and simulated using the program SDTrimSP [8, 9]. A significant amount of helium is implanted upon irradiation, leading to a fluence-dependent mass change rate. When an equilibrium of implantation and rerelease is reached the mass loss due to sputtering of target material is observed. This saturation happens after a fluence of about 1021 ions per m2, which corresponds to an irradiation by the solar wind of several hundred years on the surface of Mercury [3]. The study shows that helium is mobile during ion irradiation, and released thermally from the sample at about 400K. Combining TDS results and measurements of the mass change, the helium volume abundance after saturation was estimated to about 10-15%. The results of this study therefore provide a more detailed understanding of the interaction between helium from solar wind and Mercury analogues.References:[1] Hapke B.: J. Geophys. Res. Planet., 106, 10039, 2001.[2] Noble S.K., et al.: Sol. Syst. Res. 37, 31, 2003.[3] Wurz P., et al.: Planet. Space Sci., 58, 1599, 2010.[4] Benkhoff J., et al.: Planet. Space Sci. 58, 2, 2010.[5] Sasaki S., et al.: Adv. Space Res., 33, 2152, 2004.[6] Hartle R., et al.: J. Geophys. Res., 80, 3689, 1975.[7] Moro M.V., et al.: Thin Solid Films, 686, 137416, 2019.[8] Mutzke A., et al.: IPP Report, 2019.[9] Szabo P.S., et al.: Icarus, 314, 98, 2018.