Self‐consistent multifluid MHD simulations of Europa's exospheric interaction with Jupiter's magnetosphere

Abstract

The Jovian moon, Europa, hosts a thin neutral gas atmosphere, which is tightly coupled to Jupiter's magnetosphere. Magnetospheric ions impacting the surface sputter off neutral atoms, which, upon ionization, carry currents that modify the magnetic field around the moon. The magnetic field in the plasma is also affected by Europa's induced magnetic field. In this paper we investigate the environment of Europa using our multifluid MHD model and focus on the effects introduced by both the magnetospheric and the pickup ion populations. The model self‐consistently derives the electron temperature that governs the electron impact ionization process, which is the major source of ionization in this environment. The resulting magnetic field is compared to measurements performed by the Galileo magnetometer, the bulk properties of the modeled thermal plasma population is compared to the Galileo Plasma Subsystem observations, and the modeled surface precipitation fluxes are compared to Galileo Ultraviolet Spectrometer observations. The model shows good agreement with the measured magnetic field and reproduces the basic features of the plasma interaction observed at the moon for both the E4 and the E26 flybys of the Galileo spacecraft. The simulation also produces perturbations asymmetric about the flow direction that account for observed asymmetries.

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

“…All other models that have been applied to E26 without a plume (Rubin et al, 2015;Schilling et al, 2007) as well as with a plume (Blöcker et al, 2016) produced a similar outbound depletion in B y as our model. Comparison to the pure induction signal (light blue line) illustrates that the inbound B y signature is generated when the dipole field is compressed by the plasma interaction, thereby amplifying the perturbations associated with an induced dipole field alone.…”

“…We use similar magnetospheric upstream parameters as Rubin et al (2015) and Blöcker et al (2016) to facilitate a comparison to their results for the E26 flyby. Since the bulk velocity of the (nearly) corotating plasma relative to Europa is not constrained through observations from E26, we use a value of u 0 = 100 km/s in agreement with Bagenal et al (2015).…”

“…Sputtering of Europa's surface is not uniform: Pospieszalska and Johnson (1989) as well as Cassidy et al (2013) showed that the sputtering rate decreases from the trailing hemisphere toward the leading hemisphere. Therefore, for the neutral density distribution, we use an analytical description similar to the model of Rubin et al (2015). The density profile in the trailing n T and leading n L hemispheres reads…”

“…A single, but broader, plume could explain the observations equally well. Mass loading of the magnetospheric plasma by Europa's ionosphere decelerates the impinging flow and deflects it around the moon (e.g., Rubin et al, 2015). Subsequently, Sparks et al (2016Sparks et al ( , 2017 were able to find new, equatorial locations of enhanced neutral column density through image postprocessing of available HST data.…”

The Dehydration of Water Worlds via Atmospheric Losses

“…A few notable examples include Mars (Najib et al 2011;Dong et al 2014Dong et al , 2015, Earth (Glocer et al 2009;Brambles et al 2010), Europa (Rubin et al 2015), Enceladus (Jia et al 2012), Ganymede (Paty & Winglee 2004) and comets (Rubin et al 2014;Huang et al 2016a,b). In all of these instances, the obtained theoretical results from the simulations have been shown to be in very good agreement with observations from missions such as MAVEN, Galileo and Rosetta.…”