Exogenic basalt on asteroid (101955) Bennu
Exogenic basalt on asteroid (101955) Bennu
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DOI：
10.1038/s41550-020-1195-z
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发表时间：
2020-09-21
期刊：
影响因子：
14.1
通讯作者：
Lauretta, D. S.
中科院分区：
文献类型：
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作者：
DellaGiustina, D. N.;Kaplan, H. H.;Lauretta, D. S.
近地小行星 (101955) Bennu 上有六块明亮的奇异物质巨石，从普通的小行星表面脱颖而出。这一意外的撞击记录为贝努的形成历史提供了线索。当碎石堆小行星 2008 TC(3) 于 2008 年 10 月 7 日撞击地球时，回收的岩石碎片表明此类小行星可能含有外源物质(1,2)。然而，迄今为止的航天器任务仅观察到不受碰撞破坏的大型整体小行星的外源污染(3,4)。在这里，我们报告了近地小行星 (101955) Bennu 表面存在米级外生巨石，这是 OSIRIS-REx 任务 (5) 的直径 0.5 公里的碎石堆目标，已通过光谱与 CM 碳质球粒陨石 (6) 联系起来。高光谱数据表明，外生巨石与来自 (4) 灶神星 (4) 的福华长石-锂辉石-闪长石 (HED) 陨石具有相同的独特辉石成分，灶神星是一颗直径 525 公里的小行星，经历了分化和广泛的火成岩加工 (7-9)。交付场景包括灶神星碎片直接落入本努或间接落入本努的母体，后者的破坏从内源性和外源性碎片的混合物中创造了本努。我们的研究结果表明，碎石堆小行星可以保留小行星间混合的证据，这种混合是在星子形成结束后很久在宏观尺度上发生的。因此，贝努表面上类 HED 材料的存在为内部主带的碰撞和动力学演化提供了以前未被认识到的限制。
Six bright boulders of exotic material on near-Earth asteroid (101955) Bennu stand out from the average asteroidal surface. This unexpected record of impactors offers clues to the formation history of Bennu.When rubble-pile asteroid 2008 TC(3)impacted Earth on 7 October 2008, the recovered rock fragments indicated that such asteroids can contain exogenic material(1,2). However, spacecraft missions to date have only observed exogenous contamination on large, monolithic asteroids that are impervious to collisional disruption(3,4). Here, we report the presence of metre-scale exogenic boulders on the surface of near-Earth asteroid (101955) Bennu-the 0.5-km-diameter, rubble-pile target of the OSIRIS-REx mission(5)that has been spectroscopically linked to the CM carbonaceous chondrite meteorites(6). Hyperspectral data indicate that the exogenic boulders have the same distinctive pyroxene composition as the howardite-eucrite-diogenite (HED) meteorites that come from (4) Vesta, a 525-km-diameter asteroid that has undergone differentiation and extensive igneous processing(7-9). Delivery scenarios include the infall of Vesta fragments directly onto Bennu or indirectly onto Bennu's parent body, where the latter's disruption created Bennu from a mixture of endogenous and exogenic debris. Our findings demonstrate that rubble-pile asteroids can preserve evidence of inter-asteroid mixing that took place at macroscopic scales well after planetesimal formation ended. Accordingly, the presence of HED-like material on the surface of Bennu provides previously unrecognized constraints on the collisional and dynamical evolution of the inner main belt.