Mid-Infrared Transmission Spectrum of the Almahata Sitta Meteorite

Stefanie N. Milam (1,2), S. A. Sandford (1), M. Nuevo (1), P. M. Jenniskens (2), 1. NASA Ames Research Center, 2. SETI Institute.
The mid-infrared spectra (4000-500 cm-1, i.e., 2.5-20 micron) of 27 stones from the Almahata Sitta meteorite fall are presented. Samples were prepared as standard KBr pellets with a 1:100 ratio of meteorite to KBr; typical meteorite samples were ~1-3 mg. Spectral profiles are dominated by a 10 micron SiO adsorption feature indicative of pyroxenes and olivines. These data are largely consistent with previous measurements of ureilites at these wavelengths [1]. The ratio of olivine to pyroxene varies from one stone to the next, and even between multiple samples of the same stone in some instances. Almahata Sitta has been classified as an anomalous polymict ureilite based on the extensive initial studies of a few meteorite fragments [2]. The spectra presented support this assessment and provide further insight into the bulk mineral composition of the meteorite.

References: [1] Sandford, S.A. (1993) Meteoritics 28, 579-585; [2] Jenniskens et al. (2009) Nature 458, 485-488.