灶神星表面的撞击污染和暗物质的释放
The contamination of the surface of Vesta by impacts and the delivery of the dark material
摘要：
黎明号宇宙飞船观测到灶神星表面存在暗物质，而暗物质又被证明与富含OH和H的物质有关。这种暗物质的来源已被确定为低丰度小行星，但仍有争议的是，暗物质的输送是否与少数大型撞击事件有关，是与微陨石有关，还是与灶神星上撞击物的持续长期流量有关。连续通量情景预测，灶神星吸积的外源物质中有很大一部分应该是由于类似于普通陨石的非黑暗撞击物，而这些撞击物只代表HED陨石中的少量污染物。我们探讨了连续通量的情况下，其影响的组成vestan风化层，利用数据从黎明任务和HED陨石。我们使用我们的模型表明，随机事件的情况下，和微陨石流量的情况下，连续流量的情况下的自然后果。然后，我们使用该模型来估计自LHB以来在Vesta上交付的黑暗和羟基化材料的数量，我们展示了我们的结果如何与黎明任务估计的值相匹配。我们用我们的模型来评估Fe和亲铁元素的量，连续流量的撞击物将混合在vestan风化层：关于亲铁元素，我们把注意力集中在Ni的作用。这些结果与HED陨石的Fe和Ni含量的现有数据一致，可用作今后研究黎明号飞行任务和HED陨石数据的参考系。我们的模型还不能提供一个答案，失踪的非碳污染物的命运，但我们讨论了这种差异的可能原因。
英文摘要：
The Dawn spacecraft observed the presence of dark material, which in turn proved to be associated with OH and H-rich material, on the surface of Vesta. The source of this dark material has been identified with the low albedo asteroids, but it is still a matter of debate whether the delivery of the dark material is associated with a few large impact events, to micrometeorites or to the continuous, secular flux of impactors on Vesta. The continuous flux scenario predicts that a significant fraction of the exogenous material accreted by Vesta should be due to non-dark impactors likely analogous to ordinary chondrites, which instead represent only a minor contaminant in the HED meteorites. We explored the continuous flux scenario and its implications for the composition of the vestan regolith, taking advantage of the data from the Dawn mission and the HED meteorites. We used our model to show that the stochastic events scenario and the micrometeoritic flux scenario are natural consequences of the continuous flux scenario. We then used the model to estimate the amounts of dark and hydroxylate materials delivered on Vesta since the LHB and we showed how our results match well with the values estimated by the Dawn mission. We used our model to assess the amount of Fe and siderophile elements that the continuous flux of impactors would mix in the vestan regolith: concerning the siderophile elements, we focused our attention on the role of Ni. The results are in agreement with the data available on the Fe and Ni content of the HED meteorites and can be used as a reference frame in future studies of the data from the Dawn mission and of the HED meteorites. Our model cannot yet provide an answer to the fate of the missing non-carbonaceous contaminants, but we discuss possible reasons for this discrepancy.
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