The Size-Frequency Distribution of Impact Craters in the Inner Solar System and Implications for Past and Recent Cratering Rates in the Earth-Moon System

Abstract

The shape of the size-frequency distribution for small (<&#61 1 km diameter) primary craters could be measured on Galileo imagery of the asteroids Gaspra and Ida. The data confirm the steep (cumulativedistribution index -3 to -4) distribution for craters < 1 km diameter found on the Moon, Mars, and Mercury. A comparison of impact crater size-frequency measurements on the Moon for areas younger than 3 Ga with impact crater frequencies on terrestrial cratons (400 m.y.old) through application of the crater production size-frequency distribution (calibration curve derived from measurements for the Moon) yields a discrepancy of a factor of 1.5-2 in crater frequencies for the same substrate ages (i.e., exposure times to impacts). This discrepancy can be explained by (1) incorrect scaling of lunar vs. terrestrial impact conditions and (2) partly incorrect crater production size-frequency distribution curves applied to both to the lunar and terrestrial data. A thorough analysis of the sample of Eratosthenian and Copernican craters used to establish most of the production crater size- frequency distribution curve (calibration distribution) lends support to the conclusion that the latter is the case. In the derivation of the curve, a number of especially large craters have been included that are older than the Eratosthenian era. Adjusting the distribution curve for these cases yields a much better agreement between the lunar and terrestrial cratering rates.