Space Weathering Induced Via Microparticle Impacts: 2. Dust Impact Simulation and Meteorite Target Analysis

• Published in: Journal of geophysical research. Planets 2019-04, Vol.124 (4), p.1084-1099
• Main Authors: Fiege, K., Guglielmino, M., Altobelli, N., Trieloff, M., Srama, R., Orlando, T. M.
• Format: Article
• Language: English
• Subjects: Asteroids; Chemical properties; Computer simulation; Copper; Cosmic dust; Crystallography; Darkening; Dust; dust accelerator; Electron bombardment; Fracture mechanics; Hypervelocity; Impact damage; Impactors; Infrared analysis; Infrared spectra; Infrared spectroscopy; Interplanetary dust; Iron; Meteorites; Meteors & meteorites; micrometeoroid impacts; Microparticles; Olivine; Organic chemistry; Photons; Reflectance; Silicates; Space weathering; Spectroscopy; Spectrum analysis; Velocity distribution; Wavelengths; Weathering; X-ray diffraction
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2018JE005564

The role of micrometeorite bombardment in space weathering on asteroid surfaces was studied using a 2 MV Van de Graaff accelerator. About 90,000‐ to 100,000‐micron‐ to submicron‐sized copper particles with a mass and velocity distribution similar to the interplanetary dust population were fired onto the surfaces of polished Allende CV3 chondrite and eucrite NWA 6966 samples at speeds between 1 to 70 kilometers per second. We find a clear relationship between microparticle bombardment, infrared reflectance decrease, and overall spectral reddening. Differences in impact effects due to variable particle speed, size, and structure are observed. Some Cu particles form large clusters that break up upon impact and disperse. Other impactors leave imprints on the surface, and implant or generate typical craters with rims and spallation features. Very small, fast particles generate small craters without spallation or significant crater rim. Mid‐infrared (IR) spectra (bulk and microscopic measurements of individual components), 3‐D laser microscopic images and XRD spectra from the processed and unprocessed samples were collected. Mid‐IR spectra (700–6,000 cm−1) over the entire sample surface show overall darkening of features. Microscopic IR spectra show the damage seen as reflectance decrease and spectral reddening, which is variable in the micrometer range, depending on impact density and target properties (mineralogic composition). The fine‐grained Allende matrix with predominantly Fe‐rich olivine seems less affected than coarse‐grained chondrules with Mg‐rich silicates, where darkening can reach 60%. X‐ray diffraction analysis also suggests chemical and crystallographical differences in the bombarded sample, due to impact shock. Plain Language Summary Weathering processes in space affect the surfaces of, for example, asteroids, due to the constant bombardment with electrons, ions, and photons emanating from the sun, and the ubiquitously present cosmic dust. This bombardment leads to changes in the physical and chemical properties of affected surface materials. The research presented in this paper focuses on the alteration of meteorite samples via dust bombardment. We shot nanometer‐ to micrometer‐sized copper particles with velocities of up to 70 km/s onto meteorite samples that resemble asteroid surfaces, using a dust accelerator. The samples were analyzed with mid‐infrared reflectance spectroscopy and spectra of processed and unprocessed samples were compared.