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.

The magnetic field of Jupiter (radius R J = 71,492 km) generates a magnetosphere that extends ∼50 R J at the sun-facing side and hundreds of R J at the sun-averted side (Joy et al., 2002). The magnetic dipole axis of Jupiter is inclined by 9.6° against its rotational axis, causing the magnetic field to "wobble" when viewed from a fixed point at the rotational equator. This wobble creates periodic variations in the magnetospheric field near Jupiter's Galilean satellites. Europa, the smallest of the Galilean satellites (radius R E = 1,560.8 km), orbits its parent planet at a distance of 9.38 R J , well within the magnetosphere. Europa possesses a dilute exosphere (e.g.,

We model the dynamics of energetic magnetospheric ions in the perturbed electromagnetic fields near Jupiter's moon Europa. The inhomogeneities in the fields near Europa are generated by the induced dipole field from the moon's subsurface ocean as well as the Alfvénic plasma interaction with its ionosphere and induced field. Inhomogeneities in Europa's ionosphere at various length scales generate substantial asymmetries in the mass loading process that further complicate the structure of the moon's electromagnetic environment. In our study, the electromagnetic fields near Europa are obtained from an established hybrid model, whereas a particle tracing tool is applied to analyze the precipitation of the three most abundant energetic ion species (hydrogen, oxygen, and sulfur) onto the moon's surface at various energies from 1 keV up to 5 MeV. To isolate the contributions of the induced dipole and ionospheric mass loading to the field perturbations and the resulting precipitation patterns, we consider multiple field configurations of successively increasing complexity. For ion energies in the kiloelectron volt regime, magnetic field line draping effectively shields large portions of Europa's surface against energetic ion impacts and drastically alters the shape of the precipitation patterns, compared to uniform fields. The fine structure of these patterns strongly depends on the complexity of the applied ionosphere model. Only in the megaelectron volt regime, the precipitation patterns are qualitatively similar for uniform and draped fields. However, the precipitation of megaelectron volt ions onto Europa is still not homogeneous, since the strong magnetospheric field keeps ion gyroradii much smaller than the moon's radius.

The goal of our study is to present a systematic modeling framework for the identification of water vapor plumes in plasma and magnetic field data from spacecraft flybys of Europa. In particular, we determine the degree to which different plume configurations can be obscured by the interaction of Jupiter's magnetospheric plasma with Europa's induced dipole field and its global atmosphere. We apply the hybrid model AIKEF (kinetic ions, fluid electrons) to investigate the effect of inhomogeneities in Europa's atmosphere (plumes) on the plasma interaction with the Jovian magnetosphere. To systematically assess the magnitude and structure of the perturbations associated with the plume-plasma interaction at Europa, we vary the plume location across Europa's surface while considering different symmetric and asymmetric density profiles of the moon's global atmosphere. To isolate the impact of a plume on Europa's magnetospheric environment, we also conduct model runs without any global atmosphere. To quantify the magnetic perturbations caused by plumes, we analyze the field components along hypothetical spacecraft trajectories through each plume. Conclusions of our study are (1) localized regions of stagnant flow are most indicative of the presence of a plume. (2) The visibility of plumes in the magnetic field strongly depends on the density profile (whether it is symmetric or asymmetric) of the global atmosphere. (3) The presence of an induced dipole complicates the identification of magnetic signatures associated with a plume and dominates Europa's magnetic environment in its intermediate vicinity. (4) Complex fine structures are visible in the tail of escaping plume ions.magnetospheric plasma interacts with the (time-varying) dipole field induced in the moon's subsurface ocean (Kivelson et al., 1999;Zimmer et al., 2000), which is driven by the 9.6 • tilt between Jupiter's magnetic and rotational axes. This induced dipole field is compressed at Europa's ramside and stretched at its wakeside, locally contributing to transverse currents and therefore to the Alfvén wings (Liuzzo et al., 2016). The coupling of the dipole-magnetosphere interaction and the ionospheric mass loading reduces the cross section of the Alfvén wings and generates a slight displacement of the wings with respect to the moon (Neubauer, 1999;Volwerk et al., 2007).However, the view of Europa's neutral gas environment was changed drastically when, in December 2012, Hubble Space Telescope (HST) observations of the moon's UV aurora revealed a localized surplus of UV emission intensity near its south pole, associated with an increase in oxygen and hydrogen column densities. Roth et al. (2014) showed that two water vapor plumes emanating near 180 • W 75 • S and 55 • S, each with a scale height of about 200 km, quantitatively match the HST observations. Through image postprocessing, Sparks et al. (2016) found hints of additional transient plumes, located near the south pole at 271 • W 63 • S and in the equatorial region at 275.7 • W 16.4 • S. However, subsequ...

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