Excimer Laser Experiments on Mixed Silicates Simulating Space Weathering on Mercury Iris Weber (1), Andreas Morlok (1), Marcel Heeger (2), Thorsten Adolphs (2), Maximilian P. Reitze (1), Harald Hiesinger (1), Karin E. Bauch (1), Aleksandra N. Stojic (1), Heinrich F. Arlinghaus (2), Jörn Helbert (3) (1) Institut für Planetologie (IfP), Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany (sonderm@uni-muenster.de); (2) Physikalisches Institut, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany; (3) DLR, Institut für Planetenforschung, Rutherfordstr. 2, 12489 Berlin, Germany. Abstract In this work, we present near and mid-infrared spectra of olivine-pyroxene mineral mixtures irradiated with a pulsed ArF UV excimer laser. Our experimental set- up simulates micrometeorite bombardment as one possible source of space weathering. The absence of transparency features of the irradiated samples indicates grain coarsening upon laser bombardment. Furthermore, the obvious darkening of the irradiated sample surface might be an effect of agglutination. 1. Introduction The joint ESA/JAXA mission BepiColombo to Mercury will allow the determination of the mineralogical composition of the hermean surface. Particularly the on-board mid-infrared spectrometer MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer), will measure the spectral features of the hermean surface in the 7-14 μm range, with a pixel scale of about 500 meters [1,2]. In the IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory of the Institut für Planetolo- gie in Münster we generate spectral data for the compilation of the database, which will be used for the exact interpretation of the spectral information delivered by MERTIS. Owing to the absence of an atmosphere as well as the short distance to the sun, the surface of Mercury has been subjected to space weathering (SW) of varying strength. The thin exosphere and the magnetic field allow solar wind particles and impactors of various sizes to reach its surface and modify it significantly over long periods with regard to the long exposure times. Altogether, those processes are referred to as SW [3,4]. Various authors simulated SW processes with different experimental set-ups [5,6]. However, so far most studies of analog material (except for meteorite studies) are based on mono-mineralic samples. In our study, we altered terrestrial analog mineral mixtures by pulsed-laser irradiation in order to investigate the effect of SW processes caused by macro to micro im- pactors. To study the effects of SW on infrared (IR) spec- troscopy, IR spectra were taken before and immediately after irradiation in the MERTIS-relevant mid-infrared range as well as in near-IR (NIR). Contamination is avoided by keeping the mixtures in vacuum from irradiation until IR measurements. Changes within the irradiated samples at nanometer scale are then examined with transmission electron microscopy (TEM). 2. Sample and Techniques Samples: Olivine (Ol=Fo91) from Dreiser Weiher, Germany, and pyroxene (Px=En87) from Bamble, Norway, were analyzed using an electron microprobe analyzer. For subsequent IR measurements and laser experiments, the silicates were first ground in a steel mortar and the grain size fraction from 63 μm to 125 μm was then pressed at ~ 8 bar for 10 min to obtain powder pellets (d = 5 mm, h = ~5 mm). As a starting material, mixtures of olivine and pyroxene with 70/30 and 30/70 (both in weight %) were prepared. Techniques: - Light microscopy: A polarized light microscope was used to determine the purity of the samples and to depict the irradiated surface (Fig. 1). - Electron microscopy: We characterized the samples chemically with detailed quantitative analyses by using a JEOL JXA-8530F Hyperprobe electron probe micro analyzer (EPMA) equipped with five wavelength dispersive spectrometers (WDS) at the Institute for Mineralogy in Münster. - IR spectroscopy - FTIR on bulk powders: FTIR analyses were performed with a Vertex 70v spectrometer at the IRIS laboratory in Münster. First analyses of single minerals as well as mineral mixtures were made at 20°(i) and 30°(e) with an A513 variable mirror reflectance stage. Measurements in vacuum were done in a Harrick Reaction chamber using a Praying Mantis TM diffuse reflectance stage. The EPSC Abstracts Vol. 13, EPSC-DPS2019-1325-1, 2019 EPSC-DPS Joint Meeting 2019 c  Author(s) 2019. CC Attribution 4.0 license.