The effect of progressive space weathering on the organic and inorganic components of a carbonaceous chondrite

We performed pulsed laser irradiation to simulate the progressive space weathering of three individual chips of the CM2 Murchison meteorite. After irradiation, we performed two-step laser desorption mass spectrometry to analyze alterations in the concentration, distribution, and functional group chemistry of organics in the samples. These results indicate an increase in the concentration of aromatic organic species in the irradiated regions of the samples compared to the unirradiated areas. We utilized optical reflectance spectroscopy, Fourier-transform infrared spectroscopy, and Mossbauer spectroscopy to investigate changes in the spectral characteristics of the samples as a result of simulated progressive space weathering. We observed an overall decrease in reflectance spectra of the irradiated samples. The spectra also exhibit a bluing trend after irradiation, the degree of which weakens with progressive laser exposure. Finally, we used scanning electron microscopy and transmission electron microscopy to examine changes in microstructure and chemistry of the irradiated samples. We observed vesicles and nanoparticles in the melt layers produced by laser irradiation. Our results indicate that the nanoparticle compositions evolve with increasing laser irradiation, progressing from a mineralogically diverse group towards a population dominated by Fe-Ni-sulfides. Radiative transfer models were used to examine the influence of various nanoparticle compositions on sample spectral properties, the results of which indicate nanoparticle size and mineralogy may result in competing spectral effects. We discuss the implications these experiments have for the space weathering of primitive, organic-rich asteroids.