2538 Microsc. Microanal. 27 (Suppl 1), 2021 doi:10.1017/S143192762100903X © Microscopy Society of America 2021 Investigating Space Weathering Effects on Carbonaceous Asteroids Using High-flux and Low-flux Ion Irradiation of the Murchison Meteorite Dara Laczniak 1 , Michelle Thompson 2 , Roy Christoffersen 3 , Catherine Dukes 4 , Simon Clemett 3 , Richard Morris 5 and Lindsay Keller 5 1 Purdue University - Department of Earth, Atmospheric, and Planetary Sciences, Lafayette, Indiana, United States, 2 Purdue University - Department of Earth, Atmospheric, and Planetary Sciences, United States, 3 Jacobs JETS, NASA Johnson Space Center, United States, 4 University of Virginia, Charlottesville, Virginia, United States, 5 NASA Johnson Space Center, United States Introduction: Airless planetary bodies are continuously altered by space weathering processes such as solar wind irradiation and micrometeoroid bombardment. These processes change the microstructural, chemical, and optical properties of planetary regoliths and, in turn, complicate interpretations of surface composition from remote sensing data. Previous space weathering investigations have focused primarily on lunar and ordinary chondrite materials, the latter of which have been linked to S-type asteroids [1]. However, relatively little is known about space weathering of primitive carbonaceous chondrites, which contain a combination of hydrous silicate and organic phases and are hypothesized to be fragments of C- complex asteroids [2]. To address this knowledge gap and maximize the science return of missions targeting C-complex asteroids (e.g., NASA OSIRIS-REx targeting Bennu and JAXA Hayabusa2 targeting Ryugu) [3-4], we examine the spectral, microstructural, and chemical effects of simulated solar wind weathering on a carbonaceous asteroid analog material. Here, we present the results from coordinated analyses of Murchison (CM2) meteorite slabs irradiated with 1 keV/amu H + and He + ions. Methods: Dry-cut Murchison slabs were exposed to 1 keV H + and 4 keV He + irradiation under ultra-high vacuum (10 -8 Pa). For the first set of experiments, we used a high ion flux of ~1.0x10 13 ions/cm 2 /s. H + - irradiation reached a total fluence of 8.1x10 17 H + /cm 2 (~700 yrs exposure at Bennu) while He + -irradiation reached a total fluence of 1.1x10 18 He + /cm 2 (~23,000 yrs at Bennu). For the second set, we used lower ion fluxes—6.6x10 11 H + /cm 2 /s and 3.6x10 11 He + /cm 2 /s—to more closely simulate the ion flux of actual solar wind (10 8 ions/cm 2 /s). H + -irradiation reached a total fluence of 4.0x10 16 H + /cm 2 (~20 yrs at Bennu) while He + -irradiation reached a total fluence of 2.1x10 16 He + /cm 2 (~400 yrs at Bennu). To characterize the unirradiated, H + -irradiated, and He + -irradiated surfaces, we perform five coordinated analytical techniques. Changes in surface chemistry are observed with in situ X-ray photoelectron spectroscopy (XPS) using a PHI Versaprobe III Scanning XPS. Changes in spectral slope, surface albedo, and absorption band strengths are evaluated using visible to near-infrared spectra (VNIR; 0.35 – 2.50 μm) acquired with a fiber-optic ASD FieldSpec 3 Spectrometer. Modifications to organic chemistry are investigated using microprobe two-step laser-desorption mass spectrometry (μL 2 MS). For transmission electron microscopy (TEM), we prepare four electron transparent cross sections consisting of matrix material, Mg-rich olivine, Fe-rich olivine, and pyroxene, respectively, from each H + - and He + -irradiated region using a Quanta 3D DualBeam field emission focused ion beam scanning electron microscope. Lastly, we use a JEOL 2500SE 200 kV field-emission scanning transmission electron microscope equipped with a 60 mm 2 ultra-thin window silicon drift energy dispersive X-ray (EDX) detector to examine the microstructure and composition of ion-affected rims in each FIB-section. https://www.cambridge.org/core/terms. https://doi.org/10.1017/S143192762100903X Downloaded from https://www.cambridge.org/core. IP address: 3.80.168.101, on 05 Nov 2021 at 00:39:17, subject to the Cambridge Core terms of use, available at