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Jovian magnetosphere‐Satellite interactions: Aspects of energetic charged particle loss
Author(s) -
Thomsen M. F.
Publication year - 1979
Publication title -
reviews of geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.087
H-Index - 156
eISSN - 1944-9208
pISSN - 8755-1209
DOI - 10.1029/rg017i003p00369
Subject(s) - jovian , magnetosphere , dynamo , physics , satellite , charged particle , computational physics , pitch angle , geophysics , astronomy , magnetic field , saturn , ion , planet , quantum mechanics
Observations of energetic charged particles obtained by Pioneers 10 and 11 near the orbits of the inner Jovian satellites are reviewed with particular emphasis on the implications of these observations with regard to possible models of the access of charged particles to the satellite surfaces. The observed effects on particle pitch angle distributions and the observed energy dependence of the intensity depletions seen at the satellite orbits are compared with predictions of satellite sweepup based on several different access models. The two major uncertainties which hamper the comparisons are those associated with the satellite conductivities and the ionospheric dynamo electric field power spectrum. The satellite conductivity is important because it governs the access of the particles to the satellite surface and therefore the lifetime τ; the dynamo power spectrum is important because it controls the magnitude and energy dependence of the radial diffusion coefficient. In spite of these uncertainties we can nevertheless make the following conclusions. (1) The electron pitch angle distributions at Io's orbit are compatible with expectations based on sweeping. (2) The energy dependences of the observed electron depletions at all three inner satellites (Amalthea, Io, and Europa) are incompatible with expectations based on a perfect conductor model of a satellite and its flux tube but are compatible with the energy dependence expected for perfectly insulating or partially conducting satellites; the energy dependences of the proton losses at all three satellites also appear to be compatible with absorption by an insulating or partially conducting satellite but only if certain forms of the dynamo power spectrum are assumed. (3) However, the proton losses at Io are observed to be much stronger than the electron losses, in contradiction to expectations based on sweeping. (4) The most attractive explanation for the proton‐electron discrepancy at Io is that the large proton losses at Io's orbit are principally due to enhanced pitch angle scattering in the region of higher plasma density and probably greater turbulence associated with the satellite rather than to satellite sweeping alone.