Nonrandom distribution of lunar craters

Abstract

Azimuths were plotted between all intersecting lunar craters >10 km in diameter, about 3200 pairs, directed from the center of the older crater to the center of the younger. The results are statistically nonrandom above the 90 percentile. Two broad zones of randomness were found, located approximately at the limbs of the near side of the moon. In between, plots show strong N-directed and S-directed peaks on both sides of the moon, E-directed peaks on the near side, and W-directed peaks on the far side. This is in contrast to the lunar tectonic grid, which lacks E-W components. Intermediate directions also are strongly directed to the east on the near side and to the west on the far side. Tectonic-grid directions are recognizable but weak, possibly because azimuths between overlapping craters may vary somewhat with the age of the craters. Although impact models resulting in nonrandom distribution of craters are possible, none tested so far fits the observed facts. The data presented here suggest endogenic origin of most large lunar craters. Stresses resulting from periodic lateral transfer of internal heat, probably by convection, could explain the azimuths between intersecting craters and also the similarities to, and differences from, the lunar tectonic grid. Possible terrestrial volcano-tectonic analogs of lunar craters are nonrandomly distributed. The greater complexity of terrestrial patterns reflects the complexity of terrestrial tectonic plates. The conclusions do not apply to maria and bright-ray craters, which rarely intersect, or to craters <10 km in diameter, which were not studied.