First in situ measurements of the Jovian Ionospheric ion population by the Juno JADE instrument

The Jovian Auroral Distributions Experiment (JADE) on the Juno mission measures plasma distributions using two nearly identical electron sensors and an ion sensor. The electron sensors (JADE-E) measure the electron distribution in the range of 100 eV to 100 keV and the ion sensor (JADE-I) measures the composition separated ion distributions in the range of 10 eV / q to 50 keV / q for ions with masses < 64 amu / q. The high velocity of the Juno spacecraft near perijove ( 50 km/s) allows observations of very low energy ions in the Jovian reference frame when viewing in the spacecraft ram direction, down to below 1 eV/q for protons. During the perijove passes when the spacecraft is at sub-auroral latitudes the ion observations show what are evidently two populations. The first appears to be of Iogenic origin based on its composition and velocity distribution. However, the second population appears to come directly from Jupiter itself. This population consists of low energy, light ions, largely consisting of protons. The ions have energies below 100 eV in the spacecraft frame, and extend down to the bottom of the JADE measurement range. Near the equator a low energy heavy ion population is also observed. In this study we will present the first observations of low energy ionospheric ions in the sub-auroral regions and below an altitude of 1 Rj.