Ionizations and conductances in jovian-like atmospheres driven by stellar background EUV photons

Abstract:

Stellar background EUV photons can ionize molecular species in planetary atmospheres. As stellar background photons shortward of 912 angstroms are filtered out by the interstellar medium, and as the solar photon flux is much larger, the contribution to ionization from non-solar photons is typically negligible for planets in our solar system. However, there are conditions under which ionization due to the stellar background may be important, or even dominant. Such conditions include, for example, (some) nightside ionospheres, exoplanets in distant orbits, rogue planets, and possibly brown dwarfs. In this presentation we show calculations of ionization in Jovian-like atmospheres due to stellar background EUV photons. These photons primarily ionize methane near and below the planetary homopause, generating a relatively weak, low-altitude ionospheric layer, and therefore a minimum level of residual ionization is expected for all Jovian-like planets within the solar neighborhood. The resulting ionospheric electrical conductances, while small, may be sufficient to close magnetospheric coupling currents within these planetary ionospheres.