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Constraints on Io's and Europa's atmospheres and interiors from modeling of the satellites' aurora

Periodic Reporting for period 1 - AuroraMHD (Constraints on Io's and Europa's atmospheres and interiors from modeling of the satellites' aurora)

Reporting period: 2018-08-01 to 2020-07-31

The goal of the proposed project was to derive constraints on the atmospheres and interiors of two of Jupiter's large Galilean moons from numerical modeling of the moons' aurora. The two moons - Io and its neighboring moon Europa - are among the most fascinating planetary bodies in our Solar System: Io is the most volcanically active body and Europa harbors a subsurface water ocean and experiences high water vapor plume eruptions at its surface. The moons' surfaces and atmospheres interact with the surrounded magnetized plasma (electrically charged gas) forming a complex electrodynamic interaction (see Figure 1b). The study of this interaction of the Galilean moons with their plasma environment is of particular interest because it provides information about the moons' atmospheres, interiors and magnetic surroundings and the influence of induction from subsurface oceans. We were particularly interested in the combination of two different approaches- observations of auroral emissions from the moons' atmospheres and numerical modeling of the plasma interaction- and the different data sets of in-situ measurements from the Galileo spacecraft and the data sets of aurora images from the Hubble Space Telescope. The objective of the project was to develop an advanced magnetohydrodynamic (MHD) model which self-consistently simulates the plasma interaction and aurora emissions in order to derive constraints on the distribution of Europa's and Io's atmospheres and interior layers.
Our objective was to develop an MHD model for the interaction between the Jovian magnetospheric plasma and the moons. Therefore, the goal was to modify the MHD code MPI-AMRVAC and implement a self-consistent calculation of the electron temperature and the electron density which is crucial for the modeling of the moons' aurora. We encountered numerical difficulties in the implementation of the electron temperature and were not able to finish the development of the MHD code during the project time. We performed successful simulations of Io's and Europa's plasma interaction with the code ZEUS-MP which was applied by the fellow for the moons' plasma interaction but does not account for the electron temperature. We performed a systematic parameter study of Io's plasma interaction with different upstream plasma conditions and models of Io's atmosphere and volcanic plumes in order to calculate the Poynting flux radiated away from Io and to compare the modeled variations of the Poynting flux with the variations of the emitted power of the southern auroral footprint (a set of auroral spots at Jupiter resulting from Io’s plasma interaction, see Figure 1c) (2)) derived from Juno-Ultraviolet Spectrograph (UVS) observations. With the investigation of the relation between Io’s plasma interaction and the emitted power of Io’s southern footprint at Jupiter with our MHD model, we achieved one main goal of the project and provided new findings about the properties of Io's atmosphere and how the variability of Io's atmosphere affects the Poynting flux radiated away from the moon.
Furthermore, we performed a series of simulations of Europa's plasma interaction with different models of Europa's atmosphere and atmospheric plumes (see Figure 1a) and compared the results with in-situ measurements from the Galileo spacecraft in order to derive constraints on Europa’s atmosphere. During the project we established a collaboration with H. Huybrighs, a research fellow from ESTEC-ESA, to work on the Energetic Particle Detector (EPD) data from Galileo spacecraft flybys. Therefore, he applied our MHD simulation results of Europa's plasma interaction with different atmospheres and plumes and performed further simulations of the flux of energetic protons using a Monte Carlo particle tracing method and analyzed the EPD data by comparing the data with his simulation results.
Exploitation and dissemination of the results were achieved by presentations on large international as well as small focused national conferences and meetings, and seminars in research institutions. The project was presented, e.g. at AGU fall meeting 2019 in San Francisco (USA), the MOP meeting 2019 in Sendai (Japan), or Svenska rymdforskares samarbetsgrupp (SRS) meeting 2019 in Göteborg (Sweden). The studies on Europa's and Io's plasma interaction led to two scientific papers published in peer-reviewed journals and two collaboration papers in preparation. The last half year of the project was strongly affected by the Covid-19 pandemic through a series of cancellations of meetings and workshops as well as official travel restrictions.
The outcome of the project advances the understanding of Io's and Europa's atmospheric properties and provides useful input to the planning and preparation of future spacecraft observations such as the ESA Jupiter Icy moon Explorer (JUICE) or the NASA Europa Clipper mission.
The outcome of the project in collaboration with ESTEC increased the evidence for existing water vapor plumes erupting of Europa's surface with a new data set and resulted in a new method which is useful to derive constraints on the moon's atmosphere and atmospheric inhomogeneities. Further analysis with this method and the simulation results from our model applied to Europa and Io are still ongoing.
The acquired data which was created from simulations during the fellowship will continue to achieve impact in ongoing collaborations and in upcoming projects related to the effect of different atmospheric distributions on the moons' plasma interaction.