Three Studies Of Impact Phenomena In The Solar System

Abstract

Meteoritic activity affects every body in the solar system; its effects are ubiquitous and therefore very useful in the exploration of many planetary bodies. This work addresses two different current problems associated with the use of impact phenomena in the study of other planetary bodies in our solar system. In Chapter 1 of this thesis, an original method of measuring depths and inferring cross-sectional shapes of impact craters using shadows cast within them by the Sun is developed. The method has the advantage of not requiring that the shadow-front pass through the center of the crater, as the current shadow-measuring technique does. It also has considerable advantages over the methods of stereogrammetry, which requires two images taken from different angles, and photoclinometry, which is sensitive to variations in reflectivity. Three examples providing a check of this method against real lunar impact craters, and demonstrating its utility, are provided. The rest of this work consists of two closely related studies of the effects of Mars's atmosphere, and its variations, on martian impact cratering and meteorite production rates. To date, little account has been taken of these, since the martian atmosphere has been considered too thin to have significant effects. Here, an original approach to the study of large impactor populations, and their effects on planetary surfaces, is developed and applied to Mars. The results show that for small crater sizes (2 m ? D ? 250 m) and impactor masses (10-1 kg ? m ? 107 kg), both processes depend strongly on atmospheric density. Even the current martian atmosphere is dense enough to produce meteorites of over 50 kg, and to substantially reduce small diameter (<30 m) impact cratering. Past, denser atmospheres would have had even greater effects. Therefore, Mars's atmosphere may interfere with surface age estimates based on counts of small craters, and its variations may be reflected in martian impact crater and meteorite populations.