永久阴影月球陨石坑内的水：进一步的LCROSS模拟和分析
Water Within a Permanently Shadowed Lunar Crater: Further LCROSS Modeling and Analysis
摘要：
2009年月球陨坑观测和传感卫星撞击飞行任务利用牧羊人号航天器对撞击产生的碎片羽流进行的分光观测，探测到了水冰的吸收，证实了关于Cabeus陨坑内永久阴影区存在水冰的现有假设。支持这次飞行任务的地面观测能够进一步限制碎片羽流的质量和撞击期间喷射的水冰的浓度。在这项工作中，我们探讨了额外的约束条件，以产生一个羽流模型是一致的地面观测所需的撞击前月球沉积物的初始条件。我们使用一层脏冰与冰浓度随深度增加，一层纯风化层和一层在月球表面以下约6米处的材料来匹配观察到的碎片羽流光曲线，否则在羽流中可以看到，但具有足够高的抗拉强度以抵抗挖掘。在几种可能的材料中，具有足够高的冰浓度的风化层和冰的混合物可能会产生这种行为。在最佳拟合模型中使用的垂直冰密度剖面使我们能够计算出Cabeus陨石坑内水冰的撞击前质量为$5 \pm 3.0 \times 10^{11}$ kg，月球沉积物中水的质量浓度为$8.2 \pm 0.001$ %wt，假设水冰的冰密度为0.8，月球风化层密度为1.5 g cm $^{-3}$，或水的质量浓度为$4.3 \pm 0.01$ %wt，假设月壤密度为3.0这些模型与地面观测相吻合，得出碎片羽流中风化层和水冰的质量与\emph{in situ}测量值一致，模型碎片羽流冰质量为108公斤。
英文摘要：
The 2009 Lunar CRater Observation and Sensing Satellite (LCROSS) impact mission detected water ice absorption using spectroscopic observations of the impact-generated debris plume taken by the Shepherding Spacecraft, confirming an existing hypothesis regarding the existence of water ice in permanently shadowed regions within Cabeus crater. Ground-based observations in support of the mission were able to further constrain the mass of the debris plume and the concentration of the water ice ejected during the impact. In this work, we explore additional constraints on the initial conditions of the pre-impact lunar sediment required in order to produce a plume model that is consistent with the ground-based observations. We match the observed debris plume lightcurve using a layer of dirty ice with an ice concentration that increases with depth, a layer of pure regolith, and a layer of material at about 6 meters below the lunar surface that would otherwise have been visible in the plume but has a high enough tensile strength to resist excavation. Among a few possible materials, a mixture of regolith and ice with a sufficiently high ice concentration could plausibly produce such a behavior. The vertical albedo profiles used in the best fit model allows us to calculate a pre-impact mass of water ice within Cabeus crater of $5 \pm 3.0 \times 10^{11}$ kg and a mass concentration of water in the lunar sediment of $8.2 \pm 0.001$ %wt, assuming a water ice albedo of 0.8 and a lunar regolith density of 1.5 g cm$^{-3}$, or a mass concentration of water of $4.3 \pm 0.01$ %wt, assuming a lunar regolith density of 3.0. These models fit to ground-based observations result in derived masses of regolith and water ice within the debris plume that are consistent with \emph{in situ} measurements, with a model debris plume ice mass of 108 kg.
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