Exogenic Dynamics, Cratering, and Surface Ages

Abstract

Impact craters on terrestrial planets are key to studying planetary geology and geophysics as well as the planetary evolution remaining as geologic features at a planet's surface. To best use the cratering record history and interpret the planetary evolution, one needs to combine a wide set of processes and parameters. This chapter reviews impact cratering processes, estimates of average impact velocities, and impact probabilities for terrestrial planets. The basics of the impact crater scaling are outlined at an up-to-date level, describing the correlation of a measured impact crater diameter and the mass and size of a body that created the impact structure. Scaling laws for large impact craters are compared with the results of the direct numerical modeling of impact cratering. The accumulation rate for impact craters on terrestrial planets is univocally considered to be constant (within a factor of 2) during the youngest 3 Ga of the solar system history, while crater-forming projectile flux evolution for the very earliest phase is debated and relates to the preferred solar system evolution concept. The intermediate flux is constrained by observations from the Earth's Moon. Different cratering chronology models are described. Measuring the number of accumulated craters at predefined sizes in a geologically outlined area of interest, one can estimate the relative and model absolute ages of the visible surface, assuming older surfaces accumulate larger number of craters. Possible challenges for this technique and the interpretation of measured size–frequency distributions of impact craters are discussed, including secondary cratering, atmospheric breakup, geologic activity, and target properties, which all modify the cratering record.