The Almahata Sitta polymict breccia and the late accretion of asteroid 2008 TC3

摘要: Abstract On October 7, 2008, a small asteroid named 2008 TC 3 was detected in space about 19 h prior to its impact on Earth. Numerous world-wide observations of the object while still allowed very precise determination area: Nubian Desert northern Sudan, Africa. The had pre-atmospheric diameter ∼4 m; weight is reported with values between ∼8 and 83 t, bulk density ∼2–3 g/cm , translating into porosity range ∼20–50%. Several dedicated field campaigns predicted strewn resulted recovery more than 700 (monolithological) meteorite fragments total ∼10.5 kg. These meteorites were collectively “Almahata Sitta”, after nearby train station 6, initially classified as an anomalous polymict ureilite. Further work, however, showed that Almahata Sitta not only ureilite but complex breccia containing chemically texturally highly variable fragments, including different ureilites, ureilite-related andesite, metal-sulfide assemblages related various chondrite classes (enstatite, ordinary, carbonaceous, Rumuruti-like). It shown chondrites ureilites derive from one parent body, i.e., making this object, combination remotely sensed physical parameters, loosely aggregated, rubble-pile-like object. Detailed examinations have been conducted mineral-chemical data for 110 samples collected, work remaining mandatory. study allows insights formation evolution their body. results support catastrophic disruption body re-accretion dispersed ureilitic material second generation asteroids. shows chondritic materials present region mixed newly formed asteroid. Asteroid part late-formed main belt liberated ∼20 Ma ago, finally moving Earth-crossing orbits ultimately led abundant Sitta, allow types meteorites, offer unique opportunity gain further processes our Solar System such migration, collision, mixing, (re-)accretion asteroidal bodies. Beyond that, event has potential understanding meteorite–asteroid links, which major goal science.