THE ALMAHATA SITTA POLYMICT UREILITE FROM THE UNIVERSITY OF KHARTOUM COLLECTION: CLASSIFICATION, DISTRIBUTION OF CLAST TYPES IN THE STREWN FIELD, NEW METEORITE TYPES, AND IMPLICATIONS FOR THE STRUCTURE OF ASTEROID 2008 TC3.

Introduction: The Almahata Sitta (AhS) polymict ureilite fell in 2008 when asteroid 2008 TC3 impacted over Sudan [1,2]. It is the first meteorite to originate from an asteroid that had been tracked and studied in space (with spectral classification) before impact [1,2], and provides a unique opportunity to correlate properties of meteorites with those of their parent asteroid. More than 700 monolithologic stones from the AhS fall were collected. Of those previously studied, ~70% were ureilites and ~30% were chondrites [3,4]. It has been inferred that 2008 TC3 was loosely aggregated and porous and disintegrated in the atmosphere, with only its most coherent clasts falling as stones [1,2,4-6]. However, understanding the structure of this atteroid is limited by incomplete study of the heterogeneous stones, and the loss of most of the mass of the asteroid [4]. The University of Khartoum (UOK) AhS collection contains over >600 AhS stones with find coordinates [1,7]. We are studying this collection [10,11] to determine: 1) the proportion of ureilitic to various non-ureilitic stones; 2) the distribution of types of stones in the strewn field; and 3) the compositional and physical structure of 2008 TC3. We report on 61 new stones, including a unique sample that may represent the bulk of the material lost from 2008 TC3.