Lunar crater counts

Abstract

The cumulative numbers of lunar craters on the bright uplands larger than given diameters increase lineaHy on a log-log scale as the crater diameter decreases. The line is so steep that for craters smaller than four miles wide, there has been extensive overlapping. The craters on the maria in each size range are about 15 times less frequent than on the uplands. The maria are of one general age but do show differences in age. Comparison with the flux of smaller masses in the neighborhood of the earth leads to a probable age of the maria of 2 to 3 billion years. The use of lunar maria crater counts to give the slope and the observed flux of smaller masses in the neighborhood of the earth, including the Apollo asteroids, to give absolute frequencies leads to equations for cumulative impacts on earth of objects from 102 to 1029 g in mass. All existing data indicate that the frequencies of objects capable of producing craters on earth or moon less than about 2 miles in diameter are higher than straight-line extrapolations of lunar crater counts would indicate.