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Jovian auroral secondary electrons and their influence on the Io plasma torus
Author(s) -
Thorne R. M.
Publication year - 1981
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl008i005p00509
Subject(s) - magnetosphere , physics , electron precipitation , jovian , atomic physics , electron , torus , ion , plasma , ionization , flux (metallurgy) , astrophysics , saturn , nuclear physics , materials science , geometry , mathematics , quantum mechanics , planet , metallurgy
A direct coupling is proposed between Jovian auroral energy dissipation (estimated to be as much as 10 14 W) and ultraviolet emissions (≈ 2.5 × 10 12 W) from the heavy ion torus surrounding Io. This association was motivated by the realization that there are serious discrepancies in all previous theories for either the auroral input or the energy source required to maintain hot electrons (> 10 eV) in the emitting torus. It is demonstrated that both problems can be resolved by adopting the plausible assumption that the dominant auroral precipitation occurs in an energy range yet to be reported, in particular heavy ions below 500 KeV. As these enter the atmosphere a dominant fraction of their energy is dissipated in producing secondary electrons with mean energy in the range 20‐40 eV. Most of the secondary electrons subsequently yield their energy to further ionization or excitation. However, those produced above an altitude where the atmospheric density is ∼ 10 10 cm −3 can escape into the magnetosphere. The electron heat flux to the magnetosphere can exceed 1% of the auroral dissipation if the dominant precipitation flux consists of heavy ions (O + or S + ) with an energy between 100 to 1000 KeV. This could provide the source of electron energy required to balance radiative loss from the Io torus and it would inject ionospheric H + ions into the magnetosphere at a rate (≈ 2 × 10 29 sec −1 ) comparable to the upper estimates of heavy ion injection near Io.