Magnetic Signatures of the Interaction Between Europa and Jupiter's Magnetosphere During the Juno Flyby

Based on a hybrid model of Europa's magnetospheric interaction, we provide context for the magnetic field perturbations observed by the Juno spacecraft during its only close flyby of the moon in September 2022. By systematically varying the incident flow conditions and the density profile of Europa's atmosphere, we demonstrate that the observed, large-scale signatures of magnetic field draping are consistent with a dawn-dusk asymmetry in the moon's neutral envelope. During the flyby, such an asymmetry would have enhanced the magnetic perturbations in Europa's anti-Jovian hemisphere, explaining why the spacecraft already detected strong field line draping while still several moon radii away. Conversely, a reduced neutral density in the sub-Jovian hemisphere can explain why the perturbations in the flow-aligned field component remained nearly constant as Juno approached Europa. While a dawn-dusk asymmetry in Europa's atmosphere has been predicted by theoretical work, our results provide the first in situ hints of its presence.