Multi-fluid MHD Modeling of Europa’s Plasma Interaction
 

Europa, one of Jupiter’s Galilean moons, orbits within Jupiter’s magnetosphere. Jupiter’s magnetospheric plasma and magnetic field interact with Europa’s atmosphere, ionosphere, surface, and subsurface ocean, causing strong variations in the magnetic fields and plasma near Europa. Due to these connections with the ocean and the surface, Europa’s space environment is a critical component in our understanding of the habitability of the moon. In this talk, I will cover two recent papers that investigate the variability of Europa’s magnetic and plasma environment using multi-fluid magnetohydrodynamic (MHD) simulations.
To characterize the variability of Europa’s plasma interaction caused by changes in the conditions of Jupiter’s magnetosphere, we have conducted a series of simulations using different upstream parameters that span the known range of external conditions at Europa (Harris et al., 2021). By separately tracking multiple ion fluids, we quantified the access of the Jovian magnetospheric plasma to Europa's surface and determined how that access is affected by changing magnetospheric conditions. We found that changes in the external conditions resulting from Jupiter’s tilted plasma sheet relative to Europa’s orbit lead to significant variations in the amount and spatial distribution of Jupiter’s magnetospheric plasma precipitating onto Europa’s surface. The total precipitation rate of the thermal magnetospheric ions increases with the density of the ambient plasma ranging between (1.8 – 26) × 1024 ions/s. Because sputtering of Europa’s icy surface by the thermal plasma is an important contributor to the generation of its atmosphere, the variations in the plasma precipitation as revealed by our modeling results provide important inputs for future models for Europa’s atmosphere.
Finally, we have investigated the effects of Europa’s atmosphere on its plasma interaction by conducting a parametric study in which the atmosphere model was systematically varied to quantitatively assess the role of atmosphere density and scale height in controlling Europa’s plasma interaction (Harris et al., 2022). We also show the magnetic field along trajectories representative of the locations observed by the recent Juno flyby and future Europa Clipper flybys, demonstrating that modest variations in the state of the atmosphere can cause discrepancies of 10s of nT.
Modeling of Europa’s magnetic and plasma environment is a critical component of magnetic sounding experiments as well as in situ identification of potential water plumes. These results illustrate the many factors that must therefore be accounted for over the next decade to facilitate these experiments.

Harris, C. D. K., Jia, X., Slavin, J. A., Toth, G., Huang, Z., & Rubin, M. (2021). Multi-fluid MHD simulations of Europa's plasma interaction under different magnetospheric conditions. Journal of Geophysical Research: Space Physics, 126, e2020JA028888. https:// doi.org/10.1029/2020JA028888
Harris, C. D. K., Jia, X., & Slavin, J. A. (2022). Multi-fluid MHD Simulations of Europa’s Plasma Interaction: Effects of Variation in Europa’s Atmosphere. Journal of Geophysical Research: Space Physics, e2022JA030569. https:// doi.org/10.1029/2022JA030569