The surface of the Moon is pitted with a myriad of small impact craters (Figure 1).
An important characteristic of lunar surface geology is the duration of the lifetimes of small craters. This number was first estimated by Basilevsky (1976) based on an analysis of the Lunar Orbiter and Apollo high-resolution images of the Moon and isotopic measurements of ages of the surface exposition of rock fragments sampled by the Apollo astronauts (Figure 2 and 3).
It is seen from the diagram in Figure 3 that the number of isotopically-dated craters is rather small, and it is necessary to increase the reliability of the estimations presented in this Figure. In the discussed paper (Basilevsky et al., 2018), we considered so-called secondary craters, which are relatively small ones formed by impacts of ejecta from the larger “”primary” craters.
Ages of secondary craters are the same as ages of the corresponding primary craters, so if we know the age of some primary craters, we can use its secondaries of different diameters to study how their morphological prominence depends on their size. In the discussed paper, we considered secondary craters of primary crater Copernicus (age ~800 Ma) and Tycho (~100 Ma). The considered Copernicus secondaries are shown in Figure 4.
For the considered secondary craters of Copernigus and Tycho using the LROC-NAC images, researchers made digital terrain models, and then the depth/diameter ratios (d/D) and maximum steepness of crater inner slopes were determined for the ages between 100 and 800 Ma for craters ranging in diameter from 220 to 940 m. The resulting model diagram is presented in Figure 5 (that is Figure 11c of the discussed paper).
These results allowed us to demonstrate that the diagram presented in Figure 3 is valid, although it does need further improvement.
These findings are described in the article entitled Morphometric studies of the Copernicus and Tycho secondary craters on the moon: Dependence of crater degradation rate on crater size, recently published in the journal Planetary and Space Science. This work was conducted by A.T. Basilevsky from the Vernadsky Institute and Moscow State University of Geodesy and Cartography, N.A. Kozlova, I.Yu. Zavyalov, and I.P. Karachevtseva from the Moscow State University of Geodesy and Cartography, and M.A. Kreslavsky from the University of California—Santa Cruz.
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