Escape of planetary atmospheres: physical processes and numerical models

We address the problem of the dissipation (escape) of planetary atmospheres and discuss the physical mechanisms controlling the nature of the relevant processes and review the mathematical models and numerical methods used in the analysis of this phenomenon, taking the limitations imposed by available experimental data into account. The structural and dynamic features of the aeronomy of Earth and terrestrial planets are discussed in detail; they are key in determining the energy absorption rate and the atmosphere escape rate. A kinetic Monte Carlo method developed by the authors for investigating the thermal and nonthermal processes of atmospheric escape is presented. Using this approach and spacecraft data, atomic loss rates from the Venusian and Martian atmospheres via a variety of escape processes are estimated, and their role at the current and early evolutionary stages of these planets is discussed. The discovery of exosolar planets, model studies of the dissipation of their gas envelopes, and the likely impact of the dissipation mechanisms on the planetary atmosphere and climate evolution have stimulated the study of this field and made it a topical research subject.