Portal de Periódicos da CAPES

Statistics of impact crater accumulation on the lunar surface exposed to a distribution of impacting bodies

1967; Elsevier BV; Volume: 7; Issue: 1-3 Linguagem: Inglês

10.1016/0019-1035(67)90067-x

1090-2643

Evan Harris Walker,

Space Science and Extraterrestrial Life

The considerable amount of lunar crater statistics available contains much information about the origin and age of the Moon's features. In addition, these statistics can provide information concerning the relative importance of various erosion mechanisms. In this paper we have derived the statistical distribution of craters as a function of size and of the time of exposure of the surface to impacting bodies. As the time of exposure increases, the crater distribution which initially corresponds to the distribution of impacting bodies, approaches saturation, which does not reflect the distribution of impacting bodies for most cases. An equation has been derived for the distribution of secondary craters resulting from the formation of a primary crater. This allows us to take into account the effects of secondaries on the distribution of craters on the Moon. We find that secondaries do not contribute significantly to the “Moon-wide” statistics for craters larger than 100 meters. The distribution in the lunar highlands is found to be that of a crater-saturated surface. On the other hand, Mare Cognitum is not saturated. The distribution of craters appearing in the Ranger 7 photographs suggests an age of about 1.5 × 109 years which would make the maria younger than usually supposed. For the Martian surface we feel crater saturation may have occurred, indicating that meteoric impact is the most important erosion process operating on large-scale features. It has been suggested that the Martian craters indicate that the surface of Mars is old and little water or atmospheric erosion has occurred. Others have suggested that more craters should have been observed, which would indicate a young age and extensive water and/or atmospheric erosion. We feel the age of the surface is difficult to estimate in the case of crater saturation and little can be deduced concerning the importance of water or atmospheric erosion.