Boulder degradation and exhumation at the rim of lunar kilometer-scale craters

IF 3 2区物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS

Icarus Pub Date : 2025-09-05 DOI:10.1016/j.icarus.2025.116804

Yuan Li , A.T. Basilevsky , Wing-Huen Ip

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引用次数: 0

Abstract

Previous studies have indicated that boulder exhumation results in the longstanding presence of surface boulders at crater rims throughout the lifetime of lunar maria. In our theoretical analysis, we suggest that mass-wasting processes and the negative balance zone effect of surface material movement play major roles in the exposure of shallow surface boulders. Given the numerous craters of various sizes and ages on the Moon, this specific subpopulation constitutes a considerable part of lunar surface boulders. Therefore, we conducted detailed observations of the topography and morphology of these boulder areas, and performed a boulder (> 6 m) statistical analysis to better understand the degradation processes and underlying exhumation mechanisms of these boulders.

Herein, we examined high boulder abundance areas at the rims of 79 km-scale lunar craters, whose ages are uniformly distributed across the estimated survival timescale of most meter-sized boulders (∼300 Ma). Optical image analysis did not reveal distinct topographic features indicative of regolith movement. The observed boulders, if not exogenous, have likely remained in proximity to their original emplacement and experienced minimal subsequent displacement. In these areas, boulder degradation is primarily governed by impact-induced erosion and thermal fatigue, gradually declining both boulder number density and maximum size over time. However, this overall trend is complicated by the continual exhumation of shallow subsurface boulders, which replenishes the surface population. This is supported by the longer estimated boulder half-life in our study areas (∼100 Ma), compared to previously reported values for meter-sized boulders (40–80 Ma), and by the presence of large boulders at some older craters that are comparable in size to those at younger ones. We propose that in older craters, the negative balance zone effect may dominate the exhumation process, and that boulder degradation and exhumation may reach a quasi-equilibrium state, sustaining a stable surface boulder population over the geological history of the lunar maria.

The observations and interpretations of this study provide a unique perspective on the understanding of boulder evolution processes on the lunar surface. Additionally, this study also provides useful insights for future lunar sampling campaigns.

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月球千米级环形山边缘的巨石退化和挖掘

先前的研究表明，在月球玛丽亚的整个生命周期中，挖掘巨石导致陨石坑边缘长期存在表面巨石。在我们的理论分析中，我们认为质量浪费过程和表面物质运动的负平衡带效应在浅层表面巨石的暴露中起主要作用。考虑到月球上有许多不同大小和年龄的陨石坑，这一特定的亚群构成了月球表面巨石的相当一部分。因此，我们对这些巨石区的地形和形态进行了详细的观察，并进行了巨石（> 6 m）的统计分析，以更好地了解这些巨石的降解过程和潜在的挖掘机制。在这里，我们研究了79公里规模的月球陨石坑边缘的高卵石丰度区域，其年龄均匀分布在大多数米大小的巨石（~ 300 Ma）的估计存活时间尺度上。光学图像分析并没有显示明显的地表特征表明风化运动。观察到的巨石，如果不是外源的，很可能保持在原始位置附近，并且经历了最小的后续位移。在这些地区，岩石的退化主要受冲击侵蚀和热疲劳的影响，随着时间的推移，岩石的数量密度和最大尺寸逐渐下降。然而，这一总体趋势因不断挖掘浅层地下巨石而变得复杂，这些岩石补充了地表岩石的数量。与先前报道的米大小的巨石（40-80 Ma）相比，我们研究区域估计的巨石半衰期（~ 100 Ma）更长，并且在一些较老的陨石坑中存在较大的巨石，这些巨石的大小与较年轻的陨石坑相当，这也支持了这一点。我们认为，在更古老的陨石坑中，负平衡带效应可能主导着挖掘过程，并且巨石退化和挖掘可能达到准平衡状态，在月球海的地质历史中维持稳定的表面巨石数量。这项研究的观测和解释为了解月球表面巨石的演化过程提供了一个独特的视角。此外，这项研究还为未来的月球采样活动提供了有用的见解。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Icarus 地学天文-天文与天体物理

CiteScore

6.30

自引率

18.80%

发文量

356

审稿时长

2-4 weeks

期刊介绍： Icarus is devoted to the publication of original contributions in the field of Solar System studies. Manuscripts reporting the results of new research - observational, experimental, or theoretical - concerning the astronomy, geology, meteorology, physics, chemistry, biology, and other scientific aspects of our Solar System or extrasolar systems are welcome. The journal generally does not publish papers devoted exclusively to the Sun, the Earth, celestial mechanics, meteoritics, or astrophysics. Icarus does not publish papers that provide "improved" versions of Bode''s law, or other numerical relations, without a sound physical basis. Icarus does not publish meeting announcements or general notices. Reviews, historical papers, and manuscripts describing spacecraft instrumentation may be considered, but only with prior approval of the editor. An entire issue of the journal is occasionally devoted to a single subject, usually arising from a conference on the same topic. The language of publication is English. American or British usage is accepted, but not a mixture of these.