Characterizing the spectral, microstructural, and chemical effects of solar wind irradiation on the Murchison carbonaceous chondrite through coordinated analyses

• DOI: 10.1016/j.icarus.2021.114479
• Publication Date: 2021-04-17T20:31:52Z
• Authors: D.L. Laczniak; M.S. Thompson; R. Christoffersen; C.A. Dukes; S.J. Clemett; R.V. Morris; L.P. Keller
• Keywords: Space weathering; Murchison meteorite; Regolith

We performed H+ and He+ irradiation experiments on slabs of the Murchison CM2 meteorite to simulate solar wind carbonaceous asteroids. Two separate 6 mm × regions were irradiated with 1 keV 4 He+, respectively, fluences 8.1 1017 ions/cm2 for 1018 He+. Unirradiated surfaces analyzed using X-ray photoelectron spectroscopy (XPS), visible near-infrared (VNIR; 0.35–2.5 μm), microprobe two-step laser-desorption mass spectrometry (μL2MS). also analytical field-emission scanning transmission electron microscopy (FE-STEM) focused ion beam (FIB) cross-sections extracted from olivine grains matrix material within H+- He+-irradiated regions. In situ XPS analyses suggest that results in removal most surface carbon partial reduction iron lower oxidation states. response He+-irradiation, we observe brightening (longward ~0.75 μm) reddening reflectance spectra, which is a departure typical lunar-style space weathering. Additionally, He+-irradiation have opposing effects organic content: H+-irradiation increases abundance some low-molecular-weight free species by breaking down macromolecular while causes decrease overall content cleaving bonds sputtering constituent atoms. This suggests change functional group chemistry asteroidal regolith different ways. contrast previous experimental weathering studies, an increase H2O OH− abundances our sample both types irradiation. FE-STEM energy dispersive (EDX) show complete amorphization phyllosilicates ion-affected rims, olivine, changes Si Mg concentrations at and/or near surface. discuss implications these understanding complex nature primitive, carbon-rich asteroids analyzing future returned samples Bennu Ryugu.