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    Thermal and fragmentation history of ureilitic asteroids: insights from the Almahata Sitta fall

    Herrin, J.S. and Zolensky, M.E. and Ito, M. and Le, L. and Mittlefehldt, D.W. and Jenniskens, P. and Ross, Aidan J. and Shaddad, M.H. (2010) Thermal and fragmentation history of ureilitic asteroids: insights from the Almahata Sitta fall. Meteoritics & Planetary Science 45 (10-11), pp. 1789-1803. ISSN 1086-9379.

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    The Almahata Sitta fall event provides a unique opportunity to gain insight into the nature of ureilitic objects in space and the delivery of ureilite meteorites to Earth. From thermal events recorded in the mineralogy, petrology, and chemistry of ureilites recovered from the fall area, we reconstruct a timeline of events that led to their genesis. This history is similar to that of other known ureilites and supportive of a disrupted ureilite parent body hypothesis. Temperatures of final mantle equilibrium were 1200–1300 °C, but this high-temperature history was abruptly terminated by rapid cooling and reduction associated with pressure loss. The onset of late reduction reactions and onset of rapid cooling must have been essentially simultaneous, most likely engendered by the same event. Cooling rates of 0.05–2 °C h−1 determined from reversely zoned olivines and pyroxenes in Almahata Sitta imply rapid disassembly into fragments tens meters in size or smaller. This phenomenon seems to have affected all known portions of the ureilite parent body mantle, implying an event of global significance rather than localized unroofing. Reaccretion of one or more daughter asteroids occurred only after significant heat loss at minimum time scales of weeks to months, during which time the debris cloud surrounding the disrupted parent was inefficient at retaining heat. Fragments initially dislodged from the ureilite parent body mantle underwent subsequent size reduction and mixed with various chondritic bodies, giving rise to polylithologic aggregate objects such as asteroid 2008 TC3.


    Item Type: Article
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Natural Sciences
    Depositing User: Administrator
    Date Deposited: 15 Dec 2014 11:58
    Last Modified: 02 Aug 2023 17:14


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