The unexpected surface of asteroid (101955) Bennu
The unexpected surface of asteroid (101955) Bennu
复制标题
DOI：
10.1038/s41586-019-1033-6
复制
发表时间：
2019-04-04
期刊：
影响因子：
64.8
通讯作者：
Marty, B.
中科院分区：
文献类型：
--
作者：
Lauretta, D. S.;DellaGiustina, D. N.;Marty, B.
NASA的起源，光谱解释，资源识别和安全性 - 重制探索者（Osiris-Rex）航天器最近到达近地小行星（101955）Bennu，它代表可能带来了预生物分子和挥发性水的物体到地球（1）。 Bennu是一种Lowalbedo B型小行星（2），与有机富含有机水合的碳质软管（3）相关。这样的陨石通过其母体的喷射而改变，并被大气进入和陆地微生物污染。因此，主要任务目标是将Bennu的样本返回到原始的地球 - 不受这些过程的影响（4）。 Osiris-Rex航天器携带一组复杂的仪器套件来表征Bennu的全球性质，支持选择采样站点的选择，并以次级中心量表（5-11）进行该站点的文档。在这里，我们考虑对Bennu的早期Osiris-Rex观察结果，以了解小行星的性质与前持续期望的比较并评估样本回报的前景。正如预期的那样，Bennu的整体组成似乎是水合和挥发性的。然而，与Bennu热惯性（12）和雷达极化比（13）的前碰到的模型相反，这表明通常平滑的表面被厘米尺度粒子分辨的成像揭示了意外的露面多样性。反照率，纹理，粒度和粗糙度超出了航天器设计规格。根据我们的前景知识，我们制定了一种采样策略，以靶向50米至直径的松散岩石斑块，其晶粒尺寸小于两厘米（4）。我们只观察到少数明显的无风险区域，范围为5至20米，其抽样对任务成功构成了重大挑战。
NASA'S Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer (OSIRIS-REx) spacecraft recently arrived at the near-Earth asteroid (101955) Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth(1). Bennu is a lowalbedo B-type asteroid(2) that has been linked to organic-rich hydrated carbonaceous chondrites(3). Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Therefore, the primary mission objective is to return a sample of Bennu to Earth that is pristine-that is, not affected by these processes(4). The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu's global properties, support the selection of a sampling site and document that site at a sub-centimetre scale(5-11). Here we consider early OSIRIS-REx observations of Bennu to understand how the asteroid's properties compare to pre-encounter expectations and to assess the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modelling of Bennu's thermal inertia(12) and radar polarization ratios(13)-which indicated a generally smooth surface covered by centimetre-scale particles-resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-metre-diameter patches of loose regolith with grain sizes smaller than two centimetres(4). We observe only a small number of apparently hazard-free regions, of the order of 5 to 20 metres in extent, the sampling of which poses a substantial challenge to mission success.