The ionospheres of the major planets

Abstract

Physical and chemical processes which affect the equilibrium distribution of ionization in the atmospheres of Jupiter, Saturn, Uranus and Neptune are reviewed. Current models imply readily detectable ionospheres for all four planets and suggest that protons should represent the dominant positive ion. Attention is directed to the probable importance of dissociative ionization of H2 as a source of H+. A number of potentially important loss mechanisms for H+ are discussed including a possible reaction of H+ with vibrationally excited H2. Protons may be removed efficiently at lower altitudes by reaction with CH4 and this process may offer a simple remote means for location of the turbopause.