Hydrogen from Jupiter's atmosphere in the Jovian magnetosphere

Abstract

The passage of Ulysses through Jupiter's magnetosphere presents a new opportunity to investigate the contribution to the Jovian magnetosphere of ions of atmospheric origin. A determination of the magnetospheric H ⁺/He ²⁺ flux ratio allows an estimate of the relative abundance of ionospheric material in the Jovian magnetosphere. We find that the H ⁺/He ²⁺ flux ratio, measured in the energy/charge range between 0.65 and 60 keV/e, steadily increases from a solar wind level of 25 at the magnetopause to a value of 700 at the point of closest approach, and then steadily decreases whilst approaching the magnetopause on the outbound path. We conclude from this that: (1) there is a significant solar wind component throughout the outer and middle magnetosphere; and (2) a significant fraction of the protons in the middle magnetosphere are of nonsolar origin.