On the role of electron-driven processes in planetary and cometary atmospheres

Abstract

Electron impact excitation plays an important role in the upper atmospheres of planets and their satellites and also in the comae of comets, in both energy transfer and chemistry. Emissions produced by electron impact excitation are vital in remote sensing of these atmospheres. Modeling of the processes and emissions requires knowledge of both the plasma parameters and accurate cross sections or rates for the electron impact processes. This modeling is illustrated by four examples: electron cooling by CO2 in the atmosphere of Mars, infrared emissions from CO in the atmosphere of Venus, fourth positive emissions from CO in the coma of comet Hale-Bopp and emissions due to excitation of the higher-energy states of molecular oxygen in the atmosphere of Europa. In each case the assembly of the plasma parameters and accurate electron impact cross sections is described, together with the modeling techniques applied and the significant results. These include a possible explanation for low temperatures in part of the upper atmosphere of Mars, evidence that the abundance of CO in comet Hale Bopp has been overestimated and identification of a useful parameter for remote sensing of Europa.