Fresh impact ejecta deposits on the lunar surface can be characterized as heterogeneous mixtures of boulders, cobbles, and fine-grained regolith that are deposited on the lunar surface during the impact crater formation process. Over time, the surface boulders associated with ejecta deposits break down into fine-grained regolith due to a combination of later impacts and thermal fatigue. Nonetheless, observations of old (>2.0 Ga) kilometer-scale (0.8–2.0 km) lunar impact craters in high-resolution images reveal >1 m boulders along their rims and in their near-proximal ejecta deposits on the lunar maria. Here, we use a combination of radar and thermal-infrared data from the Lunar Reconnaissance Orbiter spacecraft to show that the rims of kilometer-sized impact craters exhibit elevated rock abundances for the lifetime of the lunar maria. We interpret these results as indicating that boulders are continually being uncovered at crater rims due to downslope movement of the overlying regolith. Moreover, rocks found at crater rims that have been exhumed from depth in geologically recent times are locally derived and unlikely to have come from other areas of the Moon. Future collection of lunar samples at crater rims will serve to mitigate the potential for sample contamination from distal sources, helping to ensure accurate geologic interpretations from the collected samples.

中文翻译：

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千米级月球陨石坑边缘长时间的岩石挖掘

月球表面的新鲜撞击喷射物沉积物可以表征为在撞击坑形成过程中沉积在月球表面的巨石、鹅卵石和细粒风化层的异质混合物。随着时间的推移，由于后期撞击和热疲劳的结合，与喷射物沉积物相关的表面巨石分解成细粒风化层。尽管如此，在高分辨率图像中对古老（> 2.0 Ga）公里尺度（0.8-2.0 公里）月球撞击坑的观察显示，沿其边缘和月球海角上近端喷射物沉积物中存在大于 1 m 的巨石。在这里，我们使用来自月球勘测轨道飞行器的雷达和热红外数据的组合来表明，在月球月海的整个生命周期中，千米大小的撞击坑的边缘表现出较高的岩石丰度。我们将这些结果解释为表明，由于上覆风化层的下坡运动，陨石坑边缘的巨石不断被发现。此外，在火山口边缘发现的在地质学上最近从深处挖掘出来的岩石是本地产生的，不太可能来自月球的其他区域。未来在陨石坑边缘收集月球样本将有助于减轻来自远端源的样本污染的可能性，有助于确保对收集的样本进行准确的地质解释。在火山口边缘发现的在地质学上最近从深处挖掘出来的岩石是当地的，不太可能来自月球的其他区域。未来在陨石坑边缘收集月球样本将有助于减轻来自远端源的样本污染的可能性，有助于确保对收集的样本进行准确的地质解释。在火山口边缘发现的在地质学上最近从深处挖掘出来的岩石是局部产生的，不太可能来自月球的其他区域。未来在陨石坑边缘收集月球样本将有助于减轻来自远端源的样本污染的可能性，有助于确保对收集的样本进行准确的地质解释。