Giant impact onto a Vesta-like asteroid and formation of mesosiderites through mixing of metallic core and surface crust
Giant impact onto a Vesta-like asteroid and formation of mesosiderites through mixing of metallic core and surface crust
复制标题
对类灶神星小行星的巨大撞击以及通过金属核心和地壳混合形成中菱铁矿
DOI：
10.1016/j.icarus.2022.114949
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发表时间：
2022
期刊：
影响因子：
3.2
通讯作者：
Genda Hidenori
中科院分区：
文献类型：
--
作者：
Sugiura Keisuke;Haba Makiko K.;Genda Hidenori
中菱陨石是一种由硅酸盐和铁镍金属混合而成的石铁陨石。中陨铁硅酸盐和金属被认为分别来自一颗分化的小行星的地壳和金属核。相比之下，中菱铁矿很少包含橄榄石，而橄榄石主要包含在地幔中。虽然巨大的撞击被认为是一种可能的机制，使地壳和金属物质混合形成中陨星，但这种巨大的撞击如何在不包括地幔物质的情况下形成中陨星状物质并不明显。我们利用光滑粒子流体动力学方法对巨大撞击差异化小行星的情况进行了三维数值模拟，以研究混合物质在生成物体上的详细分布。对于目标体的内部结构模型，我们使用了从小行星灶神星的岩浆海洋结晶模型导出的薄地壳模型。我们还考虑了另一种可能的目标体内部结构，一个厚的地壳和一个大的金属核心，这是黎明号探测器对灶神星的近距离观测所提出的。在前一个模型的模拟中，金属核心的挖掘需要几乎灾难性的影响，地幔暴露在大面积的表面。因此，在其表面产生的石铁物质很可能包括地幔物质，并且很难产生具有这种内部结构的中菱铁矿状物质。相反，在后一种模型的模拟中，地幔物质仅在撞击地点暴露，即使撞击挖掘了金属核，我们证实，从这样的表面可以形成几乎没有地幔物质的表面和形成中菱铁矿样物质。因此，我们的模拟表明，一个内部结构与厚地壳和一个大的核心是更有可能作为一个中陨铁母体，而不是从传统的岩浆海洋模型推断的薄地壳内部结构。
Mesosiderites are a type of stony-iron meteorites composed of a mixture of silicates and Fe–Ni metals. The mesosiderite silicates and metals are considered to have originated from the crust and metal core, respectively, of a differentiated asteroid. In contrast, mesosiderites rarely contain the olivine that is mainly included in a mantle. Although a giant impact onto a differentiated asteroid is considered to be a probable mechanism to mix crust and metal materials to form mesosiderites, it is not obvious how such a giant impact can form mesosiderite-like materials without including mantle materials. We conducted three-dimensional numerical simulations of giant impacts onto differentiated asteroids, using the smoothed particle hydrodynamics method, to investigate the detailed distribution of mixed materials on the resultant bodies. For the internal structure model of a target body, we used a thin-crust model derived from the magma ocean crystallization model of the asteroid Vesta. We also considered, as another possible internal structure for the target body, a thick crust and a large metal core suggested from the proximity observation of Vesta by the Dawn probe. In the simulations with the former model, excavation of the metal core requires nearly catastrophic impacts and mantle is exposed over large surface areas. Thus, stony-iron materials produced on its surface are likely to include mantle materials, and it is difficult to produce mesosiderite-like materials with this internal structure. Conversely, in the simulations with the latter model, mantle materials are exposed only at impact sites, even when the impacts excavate the metal core, and we confirmed that the formation of a surface with little mantle material and the formation of mesosiderite-like materials are possible from such a surface. Therefore, our simulations suggest that an internal structure with a thick crust and a large core is more likely as a mesosiderite parent body rather than the thin-crust internal structure inferred from the conventional magma ocean model.