| Impact between and upon planetary bodies is an important process in the formation and evolution of objects in the solar system. Many of the planets and their satellites are covered by an atmosphere. These atmospheres affect impact cratering and also related impact processes. Therefore, it is important to take into account the atmospheric effects in impact processes. Moreover, the obliqueness of impact processes is important to take into account, since most possible impact angle is 45{dollar}spcirc{dollar} from the zenith. Both atmospheric effects and obliqueness of impact processes are investigated in this thesis. This thesis consists of four chapters. The first chapter describes the numerical method known as Smoothed Particle Hydrodynamics (SPH), that is used in present calculations relating to oblique impact on a planet with an atmosphere. Numerical test results are presented to demonstrate the validity of the present computer code. The three-dimensional SPH code is applied to Comet Shoemaker-Levy 9 (SL9) impact on Jupiter, particularly the disintegration of the comet in the Jovian atmosphere and the evolution of the vapor plume. This work was conducted before the impact of SL9 on Jupiter and predicted the high observational possibility from ground-based telescopes. These calculations are described in chapter II. In order to interpret the phenomena observed in the impacts, numerical predictions are compared with the observational data. These comparisons are summarized in chapter III. Chapter IV considers analytical models of the formation of radar dark and/or bright halos surrounding impact craters discovered on Venus as a result of the Magellan mission. The surface features caused by the atmospheric shock waves associated with impacts are modeled and applied to the observed Venusian radar features. |
