| Autor: |
Fassett, Caleb I., Beyer, Ross A., Deutsch, Ariel N., Hirabayashi, Masatoshi, Leight, CJ, Mahanti, Prasun, Nypaver, Cole A., Thomson, Bradley J., Minton, David A. |
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| Zdroj: |
Journal of Geophysical Research. Planets; Dec2022, Vol. 127 Issue 12, p1-12, 12p |
| Abstrakt: |
Crater degradation and erosion control the lifetime of craters in the meter‐to‐kilometer diameter range on the lunar surface. A consequence of this crater degradation process is that meter‐scale craters survive for a comparatively short time on the lunar surface in geologic terms. Here, we derive crater lifetimes for craters of <∼200 m in diameter by analyzing existing functional expressions for crater population equilibrium and production. These lifetimes allow us to constrain the topographic degradation needed at different scales to explain when craters become undetectable on equilibrium surfaces. We show how topographic degradation can be treated as a process of anomalous (scale‐dependent) topographic diffusion and find large differences in effective diffusivities at different scales, consistent with a wide range of evidence besides equilibrium behavior. Understanding the range of morphology of meter‐scale craters is particularly relevant for future exploration of the lunar surface with rovers. We illustrate expectations for the d/D distribution of small lunar craters on surfaces with negligible regional‐scale slopes. Our results imply that if volatiles are found in preserved <4 m craters and were delivered after crater formation, the volatiles must have been emplaced in the last ∼50 Ma. Given the rates of surface evolution we infer, the most likely emplacement time for any volatiles discovered at or near the surface in the interior of fresh, small craters may be much younger than this upper limit. Plain Language Summary: Impact craters are the most common landform on the Moon and form across a range of sizes and at vastly different rates. Small, meter‐sized craters form much more frequently than large, kilometer‐sized craters. After crater formation, craters start to widen, fill in, and their topographic relief is reduced due to their exposure to the lunar environment. Eventually, this infilling process is sufficient to render craters unrecognizable on the surface. The time over which this occurs is the crater lifetime, which is a function of crater diameter. This paper quantifies the crater lifetime. As suggested by some earlier workers, we show that, for 10–100 m craters, lifetime increases as a function of diameter to a power p of ∼1.1–1.3. This diverges from what would be expected for one model for how regolith on the Moon is transported ("classical diffusion"), which would have p = 2, and supports a different model ("anomalous diffusion") that implies the rate of infilling depends on the scale being considered. In this study, we also show that this model for surface evolution implies that any volatiles that end up being discovered within small fresh craters on the Moon must have gotten there recently. Key Points: The crater population in equilibrium can be combined with a production model to directly constrain crater lifetime for <∼200‐m diameter cratersWith known initial crater shapes and erasure thresholds, the effective diffusivity compatible with these crater lifetimes can be inferredIf volatiles are found in small (<4‐m) craters and were delivered after crater formation, the volatiles are <∼50 Ma old [ABSTRACT FROM AUTHOR] |
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