Inhomogeneity of asteroid 2008 TC3 (Almahata Sitta meteorites) revealed through magnetic susceptibility measurements


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Abstract– Magnetic susceptibility measurements were performed on freshly fallen Almahata Sitta meteorites. Most recovered samples are polymict ureilites. Those found in the first 4 months since impact, before the meteorites were exposed to rain, have a magnetic susceptibility in the narrow range of 4.92 ± 0.08 log 10−9 Am2 kg−1 close to the range of other ureilite falls 4.95 ± 0.14 log 10−9 Am2 kg−1 reported by Rochette et al. (2009). The Almahata Sitta samples collected 1 yr after the fall have similar values (4.90 ± 0.06 log 10−9 Am2 kg−1), revealing that the effect of 1 yr of terrestrial weathering was not severe. However, our reported values are higher than derived from polymict (brecciated) ureilites 4.38 ± 0.47 log 10−9 Am2 kg−1 (Rochette et al. 2009) containing both falls and finds, confirming that these are significantly weathered. Additionally, other fresh-looking meteorites of nonureilitic compositions were collected in the Almahata Sitta strewn field. Magnetic susceptibility measurements proved to be a convenient nondestructive method for identifying nonureilitic meteorites among those collected in the Almahata Sitta strewn field, even among fully crusted. Three such meteorites, no. 16, 25, and 41, were analyzed and their composition determined as EH6, H5, and EL6, respectively (Zolensky et al. 2010). A high scatter of magnetic susceptibility values among small (<5 g) samples revealed high inhomogeneity within the 2008 TC3 material at scales below 1–2 cm.