Measurements of the Jovian high-latitude ionospheric outflow

Abstract:

High–latitude ionospheric ions from Jupiter are observed between the magnetic latitudes bounded by the auroral oval and the Io footpoint. Cold ionospheric ions are observed when the Juno spacecraft crosses these latitudes at distances > 1.2 RJ planetocentric, and is traveling at velocities ~ 50 km/s. These ionospheric ions consist of protons with energies of a few eV. No cold plasma is observed at these altitudes poleward of the oval or equatorward of the Io footpoint. Higher energy magnetospheric ions are also seen at these latitudes. The source of the magnetospheric ions is tied to the Io torus and plasma sheet, indicated by the cut off seen in both the magnetospheric and ionospheric plasma at Io M-shells. The high latitude ionospheric protons are observed simultaneously with a loss cone in the magnetospheric ions, suggesting precipitating magnetospheric ions may contribute to heating the upper ionosphere and raising ionospheric protons to higher altitudes. The low altitudes and high velocities of the Juno spacecraft enable the Jovian Auroral Distributions Experiment Ion (JADE-I) sensor to make in situ measurements of the cold, ionospheric ions. JADE-I measures ion energies down to approximately 10 eV/q in the spacecraft frame. The spacecraft’s high velocity enables JADE to measure ions down to < 1 eV when looking into the ram direction. For reference, a 50 km/s proton has an energy of 13 eV. The cold ionospheric ions are not fully resolved by JADE-I, so forward modelling is used to determine the outflow parameters. We present in situ observations of the cold ionospheric plasma and measurements of the ionospheric outflow.