Magnetic Signatures of a Plume at Europa During the Galileo E26 Flyby

We analyze the magnetic field perturbations observed near Jupiter's icy moon Europa by the Galileo spacecraft during the E26 flyby on 3 January 2000. In addition to the expected large‐scale signatures of magnetic fieldline draping and induction, the E26 data set contains various prominent structures on length scales much smaller than the moon's radius. By applying a hybrid (kinetic ions and fluid electrons) model of Europa's interaction with the impinging magnetospheric plasma, we demonstrate that these fine structures in the magnetic field are consistent with Galileo's passage through a water vapor plume whose source was located in Europa's orbital trailing, southern hemisphere. Considering the large‐scale asymmetries of Europa's global atmosphere alone is not sufficient to explain the observed magnetic signatures. Combined with the recent identification of a plume during the earlier E12 flyby of Galileo, our results provide strong evidence that plume activity at Europa was a persistent phenomenon during the Galileo era. Plain Language Summary Observations by the Hubble Space Telescope have revealed the presence of water vapor plumes at Jupiter's icy moon Europa. However, in contrast to the Enceladus plume, the occurrence of plumes at Europa seems to be a transient phenomenon. The mechanism governing the times and locations of these emissions is still unknown. In addition to telescope observations, magnetic field data collected near Europa can be applied as a tool to search for plumes. Since Europa is located within Jupiter's magnetosphere, the moon is continuously exposed to a flow of magnetized plasma with a relative velocity around 100 km/s. The interaction of this plasma with a plume at Europa will locally deflect the magnetospheric flow, thereby generating characteristic deformations of Jupiter's magnetic field. We have revisited magnetic field observations acquired by the Galileo spacecraft during its E26 flyby of Europa on 3 January 2000. By using a plasma simulation model, we demonstrate that the magnetic perturbations observed near Europa are indicative of a water vapor plume in the moon's trailing hemisphere. The source of this plume was located near the Butterdon Linea at Europa's surface. This finding is highly relevant for the planning of synergistic measurements during the upcoming Europa Clipper mission. Key Points Magnetic perturbations seen during Europa flyby E26 consistent with Galileo's passage through a plume in the southern trailing