水星上的巨石
Boulders on Mercury
摘要：
行星、卫星和小天体表面的巨砾及其地质联系提供了有关表面过程的重要信息。我们分析了所有可用的水星表面图像，这些图像具有足够的分辨率和质量来检测巨石，我们绘制了所有观察到的巨石。可检测到的巨石的尺寸下限为~5 m。在水星上发现的所有巨石都与直径数百米或更大的新撞击坑有关。我们将水星上的巨石数量与月球上相同大小的巨石数量进行了比较，发现水星上的巨石数量比月球高地少30倍。由于源数据的限制，这种精确的定量估计本质上是不准确的;然而，水星上巨石的相对稀有性可以坚定而可靠地建立。我们讨论了观察到的差异的可能原因。由于水星上的昼夜温度循环，更高的热应力和更快的材料疲劳可能会导致巨石表面上分米的快速崩解，从而导致更快的巨石消失;然而，这些因素本身不能解释所观察到的差异。水星上拟议的较厚的风化层可能会显着降低巨石生产率。水星上较高的微陨石流量可能会导致微陨石磨损成为巨石退化的主要因素;这种高磨损率可能会缩短巨石的寿命。这些因素的结合似乎能够解释水星上巨石的相对罕见。
英文摘要：
Boulders on the surfaces of planets, satellites and small bodies, as well as their geological associations, provide important information about surface processes. We analyzed all available images of the surface of Mercury that have sufficient resolution and quality to detect boulders, and we mapped all the boulders observed. The lower size limit of detectable boulders was ~5 m. All boulders found on Mercury are associated with fresh impact craters hundreds of meters in diameter or larger. We compared boulder population on Mercury with population of boulders of the same size on the Moon, and found that boulders on Mercury are ~30 times less abundant than in the lunar highlands. This exact quantitative estimate is inherently inaccurate due to the limitation in the source data; however, the significant relative rarity of boulders on Mercury can be firmly and reliably established. We discuss possible causes of the observed difference. Higher thermal stresses and more rapid material fatigue due to diurnal temperature cycling on Mercury may cause rapid disintegration of the upper decimeters of the boulder surface and thus contribute to more rapid boulder obliteration; however, these factors alone cannot account for the observed difference. A proposed thicker regolith on Mercury is likely to significantly reduce boulder production rate. A higher micrometeoritic flux on Mercury is likely to result in micrometeoritic abrasion being a dominant contributor to boulder degradation; this high abrasion rate likely shortens the boulder lifetime. A combination of these factors appears to be able to account for the relative rarity of boulders on Mercury.
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