Slopes of Lunar Crater Size-Frequency Distributions at Copernican-Aged Craters

Craters on the lunar surface can provide valuable information about the timing and sequence of surface-forming processes on the Moon. A commonly used method for age determination is the analysis of the crater size-frequency distribution (CSFD) to which a production function (PF) is fitted that represents the size-frequency distribution of the impactors. However, the commonly used PF of Neukum (1983) is valid for crater diameters between 10 m and 300 km. Neukum et al. (2001, ) revised the PF for crater diameters of 100 m-200 km. However, it is suggested to also be valid for the diameter range of 10 m-300 km as well. To assess whether we can extend a PF to craters <= 10 m in diameter, we investigated the slopes of the CSFDs of small craters formed on ejecta of young Copernican-aged craters Giordano Bruno, Moore F, North Ray, and South Ray. A PF for smaller diameters would allow dating of young geological units, which are typically small, and would reduce the statistical error in age determinations, since smaller craters are more abundant. However, small craters are strongly influenced by geological factors, such as target properties, crater degradation, and secondary craters. For craters between 10 and 20 m we obtain a steeper CSFD slope than Neukum's proposed -3 slope (cumulative), whereas for craters <= 10 m the slope is about -3. We conclude that the PF of Neukum (1983) provides a reasonable CSFD slope for smaller craters, although it was not developed for this crater diameter range.