Spectral and chemical effects of simulated space weathering of the Murchison CM2 carbonaceous chondrite

M.S. Thompson, M.J. Loeffler, R.V. Morris, L.P. Keller, R. Christoffersen

In Press, Accepted Manuscript, Available online 18 September 2018


• Space weathering of a carbonaceous chondrite simulated via pulsed laser irradiation
• Reflectance spectra of the melt and vapor deposits show strong reddening
• The reflectance spectrum of the irradiated meteorite surface is darkened
• TEM analyses reveal a compositionally diverse nanoparticle population
• Results suggest a departure from lunar-style space weathering”

“We performed pulsed-laser irradiation of a chip of the CM2 Murchison carbonaceous chondrite meteorite to simulate micrometeorite impacts on carbonaceous asteroids. Optical reflectance spectroscopy and by transmission electron microscopy were performed to characterize the unirradiated and irradiated samples and vapor and melt deposits collected on a glass slide ∼7 mm from the surface of the sample. The spectrum of the deposit on the glass slide shows a red slope between 0.35-2.5 µm, while the irradiated surface of the meteorite shows only slight darkening over the same spectral range. We identified predominant melt products and vesiculated textures in the glass slide deposit, in the fine-grained matrix of the meteorite, and in individual mineral phases of the meteorite chip. Extracted focused ion beam (FIB) sections from the matrix material, an olivine grain, a pentlandite grain, and from the glass slide deposit were analyzed by scanning transmission electron microscopy (STEM). Microstructural and chemical analyses based on the STEM observations show widespread melting and the formation of Fe-bearing nanoparticles (including prevalent Fe-Ni-sulfides) across the surface of the meteorite. The section extracted from the glass slide revealed nanoparticles embedded in a chemically and microstructurally complex deposit, which likely formed as a result of both melting and vaporization processes. These analyses reveal a significantly more compositionally diverse population of nanoparticles compared to what is observed in lunar or ordinary chondritic space weathered samples. We discuss the implications these results have for the space weathering of carbonaceous asteroids and their importance for understanding the surface processes on primitive bodies.”