On The Energy Per Ion Pair In The Upper Atmospheres of Planets

The mean energy expended in a collision by an electron in atmospheric gazes is a useful parameter for fast aeronomy computations. Its inverse represents the overall efficiency of a particle or an electromagnetic radiation in ionising a gas or a mixture of gas and is thus characteristic of the species considered. Following a method proposed by Rees (1963), the ion and electron production height profiles can be calculated to derive the luminosity height profiles without having to solve a kinetic transport equation. Although computers are nowadays much faster than some decades ago when the energy per electron-ion pair was first computed, transport codes are still sparse especially when dealing with comparative planetology. Therefore, recent works still use the Rees method. The value of 35 eV has often been used although many authors have shown that it depends on the energy of the precipitated particle and on the atmospheric composition. In the present paper, we use a kinetic transport code adapted to Mars (Simon et al., 2008), Venus (Gronoff et al., 2008), Earth (Lilensten et al., 2002), Titan (Lilensten et al., 2005) and Jupiter to compute the energy per pair. We show that this parameter depends on the planet and propose different average values for each of them.