Electron Impact Ionization in the Icy Galilean Satellites' Atmospheres

TL;DR

This paper discusses electron impact ionization processes in the atmospheres of the icy Galilean satellites, providing models and data crucial for interpreting observational measurements of their ionospheres.

Contribution

It offers new fits to electron impact ionization cross sections for water-related molecules, aiding in accurate ionization rate calculations for Jovian satellite atmospheres.

Findings

Provides energy-dependent ionization cross sections for H2O, H2, O2, H, O.

Calculates ionization rates using plasma measurements and compares with solar photo-ionization.

Enhances interpretation of spacecraft and telescopic observations of icy satellites.

Abstract

Electron impact ionization is critical in producing the ionospheres on many planetary bodies and, as discussed here, is critical for interpreting spacecraft and telescopic observations of the tenuous atmospheres of the icy Galilean satellites of Jupiter (Europa, Ganymede, and Callisto), which form an interesting planetary system. Fortunately, laboratory measurements, extrapolated by theoretical models, were developed and published over a number of years by K. Becker and colleagues (see Deutsch et al. 2009) to provide accurate electron impact ionization cross sections for atoms and molecules, which are crucial to correctly interpret these measurements. Because of their relevance for the Jovian icy satellites we provide useful fits to the complex, semi-empirical Deutsch-Mark formula for energy-dependent electron impact ionization cross-sections of gas-phase water products (i.e., H2O, H2, O2, H, O). These are then used with measurements of the thermal plasma in the Jovian magnetosphere to produce ionization rates for comparison with solar photo-ionization rates at the icy Galilean satellites.