Mars/moon Cratering Rate Ratio Estimates

This article presents a method to adapt the lunar production function, i.e. the frequency of impacts with a given size of a formed crater as discussed by Neukum et al. (2001), to Mars. This requires to study the nature of crater-forming projectiles, the impact rate difference, and the scaling laws for the impact crater formation. These old-standing questions are reviewed, and examples for the re-calculation of the production function from the moon to Mars are given. 1. Crater Forming Projectiles The modern crater forming projectiles are believed to be presented by three main populations: asteroids, Jupiter-Family comets (JFC), and long period comets (LPC). These bodies have different kinds of orbits, and physical and mechanical properties. According to Shoemaker and Wolfe (1982), for Earth and for all terrestrial planets the JFC impacts play a minor role in the formation of impact craters. Asteroids and long period comets may give comparable contributions to the modern cratering rate. However, the long period comets’ flux in terms of mass of the projectiles is currently poorly known. Shoemaker and Wolfe (1982) used measurements of the LPC nuclear size by Roemer (1965, 1966), Roemer and Lloyd (1966) and Roemer et al. (1966), and the astronomically estimated frequency of fly-by through the solar system. As the estimated cratering rate from these assumptions was too high, Shoemaker and Wolfe (1982) ascribed the overestimate to the unresolved comae of measured LPCs, and drastically decreased the published nuclear diameter estimates by a factor of 3. Consequently, knowing the average probability and velocity of LPC impacts very well, there remains a severe problem of not knowing both the size distribution and the formation rate of impact craters by LPCs. According to Neukum et al. (2001), the size-frequency distribution (SFD) of craters at best corresponds to the one of asteroids. At the same time, known estimates for the SFD of comet nuclei contradict the planetary cratering records (Shoemaker and Wolfe, 1982). Thus, as a first approximation this article compares the moon and Mars only for asteroid impacts. Most asteroids occupy the area between the orbits of Mars and Jupiter, named the Main Belt (MB; see Binzel et al., 1989, for a review and database). The relatively small sub-population of asteroids that currently cross the orbits of terrestrial planets are called Planet Crossing Asteroids (PCA). Chronology and Evolution of Mars 96 87–104, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.