Bidirectional visible-NIR and biconical FT-IR reflectance spectra of Almahata Sitta meteorite samples

Abstract– Bidirectional visible and near-infrared and off-axis biconical Fourier transform infrared reflectance spectra of Almahata Sitta meteorite stone samples, fragments of asteroid 2008 TC3, have been measured. These meteorites represent the first freshly fallen polymict ureilites available for such studies. Although the chip samples show varying degrees of terrestrial weathering depending on their environment on Earth, many of them are much fresher than other ureilites known to date. The majority of the Almahata Sitta chips studied here show only a weak near-UV absorption, a flat spectrum at visible and near-IR wavelengths, and varying depths of the 1 and 2 μm pyroxene and olivine bands. The astronomical reflectance observations of the asteroid 2008 TC3 over the range 0.55–1.0 μm provide a constraint on what a combination of the measured spectra can represent in the surface reflectance of the asteroid over the 0.32–2.55 μm range measured in this study. Most of the recovered samples of Almahata Sitta have textures and albedos similar to stones #27 (largest recovered fragment), #4, and #47. Results of linear least-square fits of the asteroid 2008 TC3 spectrum with two sets of the meteorite spectra suggest that the asteroid had 10–12% albedo and no fine regolith on its surface. We note that other lithologies may be at the surface of other fragments of the asteroid family from which 2008 TC3 originated. In that case, reflectance spectra could vary significantly among family members.