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Abstract: One important, almost ubiquitous, tool for understanding the surfaces of solid bodies throughout the solar system is the study of impact craters. While measuring a distribution of crater diameters and locations is an important tool for a wide variety of studies, so too is measuring a crater's “depth.” Depth can inform numerous studies including the strength of a surface and modification rates in the local environment. There is, however, no standard data set, definition, or technique to perform this data‐gathering task, and the abundance of different definitions of “depth” and methods for estimating that quantity can lead to misunderstandings in and of the literature. In this review, we describe a wide variety of data sets and methods to analyze those data sets that have been, are currently, or could be used to derive different types of crater depth measurements. We also recommend certain nomenclature in doing so to help standardize practice in the field. We present a review section of all crater depths that have been published on different solar system bodies which shows how the field has evolved through time and how some common assumptions might not be wholly accurate. We conclude with several recommendations for researchers which could help different data sets to be more easily understood and compared. [ABSTRACT FROM AUTHOR]

On average, secondary impact craters are expected to deepen and become more symmetric as impact velocity ( v i) increases with downrange distance ( L). We have used high-resolution topography (1-2 m/pixel) to characterize the morphometry of secondary craters as a function of L for several well-preserved primary craters on Mars. The secondaries in this study ( N = 2644) span a range of diameters (25 m ≤ D≤400 m) and estimated impact velocities (0.4 km/s ≤ v i≤2 km/s). The range of diameter-normalized rim-to-floor depth ( d/ D) broadens and reaches a ceiling of d/ D≈0.22 at L≈280 km ( v i= 1-1.2 km/s), whereas average rim height shows little dependence on v i for the largest craters ( h/ D≈0.02, D > 60 m). Populations of secondaries that express the following morphometric asymmetries are confined to regions of differing radial extent: planform elongations ( L< 110-160 km), taller downrange rims ( L < 280 km), and cavities that are deeper uprange ( L< 450-500 km). Populations of secondaries with lopsided ejecta were found to extend to at least L ∼ 700 km. Impact hydrocode simulations with iSALE-2D for strong, intact projectile and target materials predict a ceiling for d/ D versus L whose trend is consistent with our measurements. This study illuminates the morphometric transition from subsonic to hypervelocity cratering and describes the initial state of secondary crater populations. This has applications to understanding the chronology of planetary surfaces and the long-term evolution of small crater populations. [ABSTRACT FROM AUTHOR]