近地小行星（101955）Bennu外生巨砾的OSIRIS-REx彩色图像特征
Characterization of Exogenic Boulders on Near-Earth Asteroid (101955) Bennu from OSIRIS-REx Color Images
摘要：
在近地小行星（101955）Bennu上有少量明亮的巨石，最近被确定为来自小行星（4）Vesta的eucritic物质。在这一发现的基础上，我们探索了Bennu上外源巨石的全球存在。我们的分析集中在大于1米的巨石上，这些巨石在OSIRIS-REx任务的四色MapCam数据中显示出特征性的1微米辉石吸收带。我们确认存在类似于eucrites的外生巨砾，并发现eucrites与碳质材料的混合物也是一些巨砾的可能组成。一些外生巨石的光谱特性类似于普通球粒陨石（OC）的陨石，虽然这些陨石的实验室光谱比Bennu上测量的更高，这可以解释为粒度效应，存在冲击熔体，或由于灰尘涂层与碳质材料的光学混合。我们的蒙特卡罗模拟预测，OC质量的中位数量添加到母体的Bennu是0.055%和0.037%的体积的100和200公里直径的母体，分别。如果Bennu是母体和S型射弹均匀混合的副产品，那么OC材料的等效质量将是一个直径为36至40米（或体积为24 200至33 600立方米）的球体。根据MapCam数据估计的Bennu内陆的OC物质总量略高（91 000 - 150 000立方米）。
英文摘要：
A small number of anomalously bright boulders on the near-Earth, rubble-pile asteroid (101955) Bennu were recently identified as eucritic material originating from asteroid (4) Vesta. Building on this discovery, we explored the global presence of exogenic boulders on Bennu. Our analysis focused on boulders larger than 1 m that show the characteristic 1-micron pyroxene absorption band in the four-color MapCam data from the OSIRIS-REx mission. We confirm the presence of exogenic boulders similar to eucrites and find that mixtures of eucrites with carbonaceous material is also a possible composition for some boulders. Some of the exogenic boulders have spectral properties similar to those of ordinary chondrite (OC) meteorites, although the laboratory spectra of these meteorites have a higher albedo than those measured on Bennu, which could be explained by either a grain size effect, the presence of impact melt, or optical mixing with carbonaceous material owing to dust coating. Our Monte Carlo simulations predict that the median amount of OC mass added to the parent body of Bennu is 0.055% and 0.037% of the volume of a 100- and 200-km-diameter parent body, respectively. If Bennu was a uniformly mixed byproduct of parent body and S-type projectiles, the equivalent mass of OC material would be a sphere with a diameter of 36 to 40 m (or a volume of 24,200 to 33,600 m3). The total amount of OC material in the interior of Bennu estimated from the MapCam data is slightly higher (91,000-150,000 m3).
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