Distribution of Heavy Ions in the Jovian Magnetosphere from Re-Analysis of Voyager PLS Data

Abstract:

Jupiter’s magnetosphere is populated with heavy ions produced by ionization of volcanic gases from Io. The 1979 flybys of the Voyager 1 and 2 spacecraft through the Jovian system provided in situ measurements of plasma properties by the Plasma Science (PLS) instruments. Re-analysis of the Voyager 1 and 2 PLS data, combined with constraints from EUV emissions, allow a more detailed description of the distribution of heavier ions throughout the entire Jovian magnetosphere. The PLS instrument on the Voyager spacecraft had a large angle of view, with 4 Faraday cups covering different portions of the sky. This allows for an accurate determination of the properties of the plasma, including density, temperature, and flow speed, assuming a convected Maxwellian distribution. We determine densities of S⁺, S⁺⁺, S⁺⁺⁺, O⁺, and O⁺⁺ ions mapped out to 30 R_J. Because the instrument measures a current as a function of energy/charge, there is an ambiguity in the measurement of the density of the dominant species O⁺ and S⁺⁺. To resolve this issue we use a chemistry model to constrain the relative amounts of these two species throughout the magnetosphere.