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Physical modeling for the Vis-SWIR spectrometry of the Chelyabinsk meteorite

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Title: Physical modeling for the Vis-SWIR spectrometry of the Chelyabinsk meteorite
Author(s): Martikainen, Julia
Contributor: University of Helsinki, Faculty of Science, Department of Physics
Discipline: Astronomy
Language: English
Acceptance year: 2016
Understanding light scattering on meteorite surfaces is difficult. Multiple factors affect the reflectance spectra of meteorites, such as space weathering, terrestrial weathering, and shocks. The main focus of this thesis was to investigate how shock induced iron changes meteorite spectra. The reflectance spectra of 30 meteorite pieces were measured with the University of Helsinki spectrometer in the wavelength range of 300 to 2500 nm. A principal component analysis (PCA) was performed on the spectra and the results were compared with previous studies carried out by Pentikäinen et al. (JQSRT, 146, 2014) and Gaffey (NASA PDS, 2001). The analyses show that HED meteorites can be separated from chondrites. However, more HED measurements are needed to verify the validity of the results. The effects of shock induced iron on meteorite spectra were modeled with the SIRIS3 (Muinonen et al., 2009) light-scattering program. Three different spectra of the Chelyabinsk meteorite were modeled, each of them having experienced a different degree of shock, and thus representing a different lithology: light-colored lithology was modeled as 10% air particles in olivine, dark-colored lithology as 10% iron particles in olivine, and impact-melt lithology as 5% air particles and 5% iron particles in olivine. The modeled spectra were then compared with the spectral measurements of the three lithologies of the Chelyabinsk meteorite. The compability of the measured and the modeled spectra was fair. In general, a higher iron occurrence makes the spectra darker and more flat. The differences between the modeled and the measured spectral shapes of the impact-melt and light-colored lithologies are caused by the absence of pyroxene in the simulations, whereas the modeled and the measured spectral shapes of the dark-colored lithology are different because the occurrence of iron in the measured spectrum is probably higher.

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