Space weathering induced via micro–particle impacts – Part 2: Dust impact simulation and meteorite target analysis

1,2K. Fiege, 2M. Guglielmino, 3N. Altobelli, 2M. Trieloff, 4R. Srama, 1T. M. Orlando
Journal of Geophysical Research, Planets (in Press) Link to Article []
1Georgia Institute of Technology, Atlanta, GA, USA
2Universität Heidelberg, Klaus–Tschira–Labor für Kosmochemie, Institut für Geowissenschaften, Heidelberg, Germany
3ESA, European Space Agency, Madrid, Spain
4Institut für Raumfahrtsysteme, Universität Stuttgart, Stuttgart, Germany
Published by arrangement with John Wiley & Sons

The role of micrometeorite bombardment in space weathering on asteroid surfaces was studied using a 2 MV Van–De–Graaff accelerator. About 90000–100000 micron– to sub–micron 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 km s−1. We find a clear relationship between micro–particle 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, implant or generate typical craters with rims and spallation features. Very small, fast particles generate small craters without spallation or significant crater rim. Mid–IR–spectra (bulk– and microscopic measurements of individual components), 3D–Laser microscopic images and XRD–spectra from the processed and unprocessed samples were collected. Mid–IR–spectra (700–6000 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 μ–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%. XRD–analysis also suggests chemical and crystallographical differences in the bombarded sample, due to impact shock.


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