Ionospheric conductances at the giant planets of the Solar System:a comparative study of ionization sources and the impact of meteoric ions

TL;DR

This study compares ionospheric conductances across the four giant planets, highlighting the role of meteoric ions and various ionization sources in influencing magnetosphere-ionosphere coupling.

Contribution

It introduces a generic ionospheric model to evaluate the impact of meteoric ions and ionization sources on conductances at all four giant planets, extending previous Jupiter-focused research.

Findings

Meteoric ions significantly contribute to conductances at Jupiter, Saturn, Uranus, and Neptune.

Ionization by precipitating electrons also affects conductances, especially at lower energies.

Weaker magnetic fields in outer planets limit meteoric ions' influence on magnetosphere-ionosphere interactions.

Abstract

The dynamics of giant planet magnetospheres is controlled by a complex interplay between their fast rotation, their interaction with the solar wind, and their diverse internal plasma and momentum sources. In the ionosphere, the Hall and Pedersen conductances are two key parameters that regulate the intensity of currents coupling the magnetosphere and the ionosphere, and the rate of angular momentum transfer and power carried by these currents. We perform a comparative study of Hall and Pedersen conductivities and conductances in the four giant planets of our Solar System - Jupiter, Saturn, Uranus and Neptune. We use a generic ionospheric model (restraining the studied ions to H3+, CH5+, and meteoric ions) to study the dependence of conductances on the structure and composition of these planets' upper atmospheres and on the main ionization sources (photoionization, ionization by precipitating electrons, and meteoroid ablation). After checking that our model reproduces the conclusions of Nakamura et al. (2022, https://doi.org/10.1029/2022JA030312) at Jupiter, i.e. the contribution of meteoric ions to the height-integrated conductances is non-negligible, we show that this contribution could also be non-negligible at Saturn, Uranus and Neptune, compared with ionization processes caused by precipitating electrons of energies lower than a few keV (typical energies on these planets). However, because of their weaker magnetic field, the conductive layer of these planets is higher than the layer where meteoric ions are mainly produced, limiting their role in magnetosphere-ionosphere coupling.