ON THE DISTRIBUTION OF LARGE LUNAR CRATERS,

The size distribution and location of all the craters of classes 1, 2, and 3 larger than 25 km in diameter on the front face of the moon were studied. The diameter distribution of the craters follows approximately the distribution that would be expected from meteoritic impact. Lateral variations in cratering over the lunar surface were determined by dividing the lunar disk into 172 equiareal zones, each of approximately 76,900 sq km. The number of craters, their average diameter and the sum of their diameters were measured in each zone. When these parameters are contoured on the lunar surface, they outline not only the maria but also areas on the terrae otherwise indistinguishable. On the terrae the amount of cratering is not random highly cratered areas occur clustered together with a correlation coefficient of 0.776. Lateral variations in size distribution were studied by dividing the front face of the moon into 9 zones, each of which has at least 60 large craters and follows approximately the physiography. The main variations are due to the maria and terrae distribution however, differences in the terrae are also indicated. It is concluded that meteoritic impact cannot offer all the answers to the origin of lunar craters. Either the craters are predominantly volcanic, or some endogenic control on the size of an impact crater exists. Author