Investigating the MIR spectral features of an Allende meteorite powder mixed with KBr

Analyzing the spectroscopy of the Allende meteorite gives us the opportunity to compare its spectra with the spectra of terrestrial minerals. The spectra of an asteroid or meteorite do not always match the spectra of the terrestrial minerals it is composed of. Our goal is to compare the mid-infrared (MIR; 5-35 μm) reflectance spectra of Allende with several anhydrous silicates to see how much they differ. The silicates are mixed with potassium bromide (KBr), which is a MIR transparent salt that is used to simulate regolith porosity. Before we make our comparisons, our first step is to understand the spectra of Allende. To do this, we first ground and sieved a sample of the Allende meteorite into three particle sizes: 0-20 μm, 20-45 μm, 45-63 μm. Since our silicates are mixed with KBr, we also mixed each of our samples with KBr ranging from 0%-90%, with 10% increments. The MIR reflectance spectra for each sample was taken using a Fourier transform infrared spectrometer, and the spectra of each sample were analyzed. Our results show that reflectance increases with increased KBr mixtures, which is consistent with previous studies. We also found that the 0-20 μm Allende powder with 0%, 10%, and 20% KBr mixtures have reflectance features with much greater spectral contrast compared to the rest of the samples, which was unexpected. A preliminary analysis suggests that these enhanced features are a result of the sample being tightly packed. Researchers have shown that by packing a powder to reduce its bulk porosity, surface scattering increases which enhance its spectral features. We tested this by calculating the porosity of each sample and found that the 0-20 μm powder with 0%, 10%, and 20% KBr mixtures have the lowest porosities out of all the samples. Thus, our results suggest the 0-20 μm sample was more packed compared to the larger two grain size bins. Our future work will involve investigating the cause of the packing and why we do not see the same spectral features in the other samples.