Earth and Mars crater size frequency distribution and impact rates:   Theoretical and observational analysis
  A framework for the theoretical and analytical understanding of the impact crater-size frequency distribution is developed and applied to observed data from Mars and Earth. The analitical model derived gives the crater population,N, as a function of crater diameter,D, and age, taking into consideration the reduction in crater number as a function of time, cause by the elimination of craters due to effects, such as erosion, obliteration by other impacts, and tectonic changes. We are also able to estimate the rate of impacts as a function of D and the kinetic energy, E, of the impactors. In particular, for energies of one megaton or larger we find near one impact every three years for Mars, an interesting and concerning result for future Mars explorations. The corresponding calculations for our planet give a probability of one impact per 15 years, while for a Tunguska like event, of about E=10 megatons, an estimate of one per century is obtained for Earth. The model allows the derivation of an expression that gives the number of craters observed today as a function of D and age. The application of this expression to the Earth`s crater data shows a remarkable agreement between theory and observations. 
William Bruckman, Abraham Ruiz, Elio Ramos
astro-ph.EP