小行星（4）Vesta上橄榄石的外生来源探讨
Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta
摘要：
在灶神星上发现橄榄石很有趣，因为它可能为我们太阳系历史早期的行星分化提供重要的见解。地面和哈勃太空望远镜（HST）对小行星（4）灶神星的观测表明其表面存在橄榄石。近年来，在灶神星发现的富含橄榄石的HED陨石加强了这些观测。然而，对美国宇航局黎明号航天器数据的分析表明，这个含有橄榄石的单元实际上是奥皮亚陨石坑喷出物中的撞击熔化物。缺乏广泛的地幔橄榄石，暴露在形成的19公里深的雷希尔维亚盆地在灶神星的南极，进一步复杂化这一情况。Ammannito等人，（2013年a）报告说，在黎明号上使用可见光和红光光谱仪（VIR）从地幔中挖掘出的物质中发现了局部规模的富含橄榄石的单元。在这里，我们探索替代来源的橄榄石在北半球的灶神星的VIR仪器使用实验室光谱测量陨石的数据进行重新分析。我们认为，这些橄榄石曝光可以解释为富含橄榄石的外生物质的交付。基于我们的光谱带参数分析，缺乏这些富含橄榄石的地形和可能的地幔挖掘事件的位置之间的相关性，并支持HED陨石的观测，我们建议，在北半球看到的橄榄石可能的来源是由富含橄榄石的陨石的撞击物的残留物。最佳匹配表明，这些单位是HED材料与普通陨石混合，或与一些橄榄石为主的陨石，如R-陨石。
英文摘要：
The detection of olivine on Vesta is interesting because it may provide critical insights into planetary differentiation early in our Solar System's history. Ground-based and Hubble Space Telescope (HST) observations of asteroid (4) Vesta have suggested the presence of olivine on the surface. These observations were reinforced by the discovery of olivine-rich HED meteorites from Vesta in recent years. However, analysis of data from NASA's Dawn spacecraft has shown that this olivine-bearing unit is actually impact melt in the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole, further complicated this picture. Ammannito et al., (2013a) reported the discovery of local scale olivine-rich units in the form of excavated material from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here we explore alternative sources for the olivine in the northern hemisphere of Vesta by reanalyzing the data from the VIR instrument using laboratory spectral measurements of meteorites. We suggest that these olivine exposures could be explained by the delivery of olivine-rich exogenic material. Based on our spectral band parameters analysis, the lack of correlation between the location of these olivine-rich terrains and possible mantle-excavating events, and supported by observations of HED meteorites, we propose that a probable source for olivine seen in the northern hemisphere are remnants of impactors made of olivine-rich meteorites. Best match suggests these units are HED material mixed with either ordinary chondrites, or with some olivine-dominated meteorites such as R-chondrites.
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