Multi‐Fluid MHD Simulations of Europa’s Plasma Interaction Under Different Magnetospheric Conditions
Harris, Camilla D. K.; Jia, Xianzhe; Slavin, James A.; Toth, Gabor; Huang, Zhenguang; Rubin, Martin
2021-05
Citation
Harris, Camilla D. K.; Jia, Xianzhe; Slavin, James A.; Toth, Gabor; Huang, Zhenguang; Rubin, Martin (2021). "Multi‐Fluid MHD Simulations of Europa’s Plasma Interaction Under Different Magnetospheric Conditions." Journal of Geophysical Research: Space Physics 126(5): n/a-n/a.
Abstract
Europa hosts a periodically changing plasma interaction driven by the variations of Jupiter’s magnetic field and magnetospheric plasma. We have developed a multi‐fluid magnetohydrodynamic (MHD) model for Europa to characterize the global configuration of the plasma interaction with the moon and its tenuous atmosphere. The model solves the multi‐fluid MHD equations for electrons and three ion fluids (Jupiter’s magnetospheric O+, as well as O+ and O2+ originating from Europa’s atmosphere) while incorporating sources and losses in the MHD equations due to electron impact and photo‐ionization, charge exchange, recombination and other relevant collisional effects. Using input parameters constrained by the Galileo magnetic field and plasma observations, we first demonstrate the accuracy of our model by simulating the Galileo E4 and E14 flybys, which took place under different upstream conditions and sampled different regions of Europa’s interaction. Our model produces 3D magnetic field and plasma bulk parameters that agree with and provide context for the flyby observations. We next present the results of a parameter study of Europa’s plasma interaction at three different excursions from Jupiter’s central plasma sheet, for three different global magnetospheric states, comprising nine steady‐state simulations. By separately tracking multiple ion fluids, our MHD model allows us to quantify the access of the Jovian magnetospheric plasma to Europa’s surface and determine how that access is affected by changing magnetospheric conditions. We find that the thermal magnetospheric O+ precipitation rate ranges from (1.8–26) × 1024 ions/s, and that the precipitation rate increases with the density of the ambient magnetospheric plasma.Plain Language SummaryThe moon Europa is embedded within Jupiter’s magnetosphere, a region of space dominated by Jupiter’s powerful magnetic field. The magnetosphere is filled with charged particles (plasma) which originate mainly from Jupiter’s moon Io. Jupiter’s magnetic field and plasma circulate throughout the magnetosphere. They flow around Europa and pile up as they approach Europa’s ionosphere, a layer of plasma that surrounds the moon and partially shields the surface from the impact of Jupiter’s magnetospheric plasma. Europa’s ionosphere is generated from its atmosphere, which is in turn generated by surface sputtering, a process in which neutral particles are released when charged particles strike Europa’s icy surface.We have developed a computational model for Europa’s space environment. We used the model to study how the changing conditions of Jupiter’s magnetosphere affect the number and temperature of magnetospheric particles that are able to reach Europa’s surface. With this result we can better understand the effect of conditions in Jupiter’s magnetosphere on sputtering and, subsequently, on Europa’s atmosphere. Understanding Europa’s atmosphere and space environment will be critical for interpreting the observations of NASA’s upcoming Europa Clipper mission.Key PointsWe present a new multi‐fluid magnetohydrodynamic model for Europa’s plasma interaction, validated against data from the Galileo E4 and E14 flybysOur model estimates a thermal O+ precipitation rate of (1.8–26)×1024 ions/s over the probable range of Jovian magnetospheric conditionsThe plasma interaction causes thermal magnetospheric plasma to precipitate on Europa’s leading/downstream hemispherePublisher
University of Arizona Press Wiley Periodicals, Inc.
ISSN
2169-9380 2169-9402
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