In-Situ and Remote Observations of the Ring Current and Radiation Belt during JUICE Lunar Earth Gravity Assist

Abstract. This report presents an overview of the observations and performance of the Jovian Energetic Neutrals and Ions (JENI) and the Jovian Energetic Electrons (JoEE) belonging to the Particle Environment Package (PEP) onboard the Jupiter Icy Moon Explorer (JUICE) during its Lunar-Earth Gravity Assist (LEGA) 19–23 August 2024. Observations from the Lunar and Earth flybys are presented and discussed. While the environment around the Moon was very quiet, the Earth flyby presented a characteristic, nearly symmetric recovery phase ring current with adiabatically increasing energies with decreasing distance to Earth, and butterfly pitch-angle distributions (PADs) at high L-shells transitioning to distributions rounded around 90° pitch angle at lower L-shells. The electron radiational belt showed a double-structured outer zone, possibly from a fresh intensification, and the characteristic slot region created by loss through interactions with plasmaspheric hiss. On the outbound, JENI was operated as an Energetic Neutral Atom (ENA) camera and observed the energetic ions of the inner magnetosphere from 17.4 R_E to 150 R_E. During this period multiple intensifications were observed in the night side magnetosphere consistent with substorm injections. The LEGA observations provided useful data for further calibrating the sensors that overall showed a nominal performance.