MHD Simulations of Europa's Interaction With Jupiter's Magnetosphere During the Juno Flyby: Electron Beams in the Plasma Wake

In September 2022, the Juno mission performed its only close flyby of Europa and traversed the moon's wake at a minimum distance of similar to ${\sim} $350 km. Among other findings, the Jovian Auroral Distributions Experiment (JADE) detector onboard the spacecraft discovered intense field-aligned electron beams (similar to ${\sim} $30-300 eV) downstream of the moon. In this study, we apply a three-dimensional magnetohydrodynamic model to simulate the plasma interaction of Jupiter's magnetosphere with Europa and its atmosphere for the conditions of this flyby, and we specifically focus on the influence of the electron beams on the plasma density and the magnetic field in the moon's space environment. We include these beams in our simulations as sheets of locally enhanced ionization, and we use electron impact ionization rates of O2 ${\mathrm{O}}_{\mathrm{2}}$ derived from JADE electron measurements to characterize the sheets. We compare our results with the magnetic field and the total ion number density measurements from Juno's magnetometer and JADE detector, respectively. Our results show that the beams fill the wake downstream of Europa with newly ionized plasma, and that they generate large variations in the magnetic field which contribute partially to the observed magnetic field. Our study demonstrates that the electron beams are critical factors in shaping Europa's magnetic field and plasma environment, and thus they need to be accounted for in the data analysis of the upcoming JUICE and Europa Clipper missions.