Energetic Oxygen and Sulfur Ions in the Jovian Magnetosphere

Citation

Gehrels, Neil (1982) Energetic Oxygen and Sulfur Ions in the Jovian Magnetosphere. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/QBH7-KH81. https://resolver.caltech.edu/CaltechETD:etd-04142009-144756

Abstract

Observations of 1 to 20 MeV/nuc oxygen, sodium, and sulfur ions in the Jovian magnetosphere are reported. Measurements made by the Cosmic Ray Subsystem on Voyager 1 and 2 are used to calculate abundances and energy spectra in the region from 5 to 20 Jovian radii (R_J). The phase space density of the oxygen ions calculated from the spectra has a positive radial gradient between 6 and 17 R_J, indicating an inward diffusive flow. The diffusion coefficient upper limit at 9 R_J is ~10^-5s^-1. This limit, combined with the analysis of Voyager plasma observations by Siscoe et al. [1981], implies an upper limit to the mass loading rate near Io of ~10²⁸ ions/s.

The energetic oxygen lifetime is within an order of magnitude of the strong pitch-angle diffusion lifetime in this region, with the largest total number of particles lost between 7.5 and 12.5 R_J. It is shown that the losses are not due to geometric absorption by Io, absorption by dust grains, or energy loss in the plasma of the inner magnetosphere, and it is therefore postulated that the primary loss mechanism is pitch-angle scattering into the loss cone.

The power delivered to the Jovian atmosphere by oxygen and sulfur ions with magnetic moments greater than 70 MeV/nuc-G (E≳0.3 MeV/nuc at 10 R_J, scattered into the loss cone between 6 and 17 R_J, is ~5x10¹² W; a power comparable to the ~1.2x10¹³ W required to produce the auroral emission observed by the ultraviolet spectrometer on Voyager [Broadfoot et al., 1981]. The measured dependence of the input power on magnetic moment threshold indicates that additional power is contributed by oxygen and sulfur ions with magnetic moments less than 70 MeV/nuc-G. Since most of the particles are lost between 7.5 and 12.5 R_J, the latitudinal zone in which the most energy is deposited in the atmosphere is ~67° to ~71°.

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