The Almahata Sitta polymict breccia and the late accretion of asteroid 2008 TC3 |
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Authors: | Marian Horstmann Addi Bischoff |
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Affiliation: | Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany |
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Abstract: | On October 7, 2008, a small asteroid named 2008 TC3 was detected in space about 19 h prior to its impact on Earth. Numerous world-wide observations of the object while still in space allowed a very precise determination of its impact area: the Nubian Desert of northern Sudan, Africa. The asteroid had a pre-atmospheric diameter of ∼4 m; its weight is reported with values between ∼8 and 83 t, and the bulk density with ∼2–3 g/cm3, translating into a bulk porosity in the range of ∼20–50%. Several dedicated field campaigns in the predicted strewn field resulted in the recovery of more than 700 (monolithological) meteorite fragments with a total weight of ∼10.5 kg. These meteorites were collectively named “Almahata Sitta”, after the nearby train station 6, and initially classified as an anomalous polymict ureilite. Further work, however, showed that Almahata Sitta is not only a ureilite but a complex polymict breccia containing chemically and texturally highly variable meteorite fragments, including different ureilites, a ureilite-related andesite, metal-sulfide assemblages related to ureilites, and various chondrite classes (enstatite, ordinary, carbonaceous, Rumuruti-like). It was shown that that chondrites and ureilites derive from one parent body, i.e., asteroid 2008 TC3, making this object, in combination with the remotely sensed physical parameters, a loosely aggregated, rubble-pile-like object. Detailed examinations have been conducted and mineral-chemical data for 110 samples have been collected, but more work on the remaining samples is mandatory. |
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Keywords: | Almahata Sitta Asteroid 2008 TC3 Polymict ureilite Polymict breccia Ureilite Ureilitic andesite Enstatite chondrites Late accretion Impact mixing Ureilite parent body |
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