Universität zu Köln

Blöcker, Aljona (2017). Modeling Io's and Europa's Plasma Interaction with the Jovian Magnetosphere: Influence of Global Atmospheric Asymmetries and Plumes. PhD thesis, Universität zu Köln.

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Abstract

We apply a three-dimensional (3D) magnetohydrodynamic (MHD) model to study the influence of inhomogeneities in Europa’s and Io’s atmospheres, as, for example, water vapor plumes and volcanic plumes, on the plasma interaction with the Jovian magnetosphere. The ideal MHD equations have been extended in order to account for the effects of the moons’ atmospheres and plumes on the plasma interaction. We have included collisions between ions and neutrals, plasma production and loss due to electron impact ionization and dissociative recombination. Moreover, electromagnetic induction in a subsurface water ocean was also considered by the model in modeling of Europa’s plasma interaction. In addition to the MHD model we apply an analytic model based on the model of Saur et al. (2007) to understand the role of steep gradients and discontinuities in Europa’s interaction. We find that Europa’s global atmosphere weakens the effect of the hemisphere coupling and generates steep gradients in the magnetic field. Volcanic eruptions on Io and water vapor plumes on Europa locally enhance the neutral density of the atmosphere and thus modify the plasma interaction. We show that an inhomogeneity near the north or south pole affects the plasma interaction in a way that a pronounced north-south asymmetry is generated. We find that an Alfvén winglet develops within the main Alfvén wing on that side where the inhomogeneity is located. Since Europa’s atmosphere is much thinner (by a factor of 100 compared to Io’s atmosphere) we show that dense atmospheric inhomogeneities affect the Alfvénic far-field much stronger compared to Io. At Europa the plasma velocity experiences a decrease up to 95% of the upstream velocity in the Alfvén winglet and a decrease up to 60% of the upstream velocity in the ambient Alfvén wing. Whereas at Io the plasma flow is decelerated by up to 93% in the Alfvén winglet and by more than 80% in the ambient Alfvén wing. Simultaneously, the Alfvén waves perturb also the magnetic field in the Alfvénic far-field so that the magnetic field perturbations are stronger in the Alfvén winglet than in the ambient Alfvén wing. The global form of the Alfvén wings is unchanged because the Alfvén velocity in the far-field is uninfluenced by the distribution of the neutral density in the atmosphere. Additionally to the effect of volcanic plumes on Io’s plasma interaction, we analyze the role of volcanic plumes on the supply rate of the Io plasma torus. We estimate that the contribution to the mass loading by the volcanic plumes is nearly negligible compared to the total mass loading rate of the global atmosphere and that the ejected neutrals, associated with the plume, contribute by less than 7 % to the total atmospheric sputtering rate. Furthermore, we apply our MHD model to analyze the effects of an asymmetric atmosphere on the plasma interaction. Therefore, we use different atmosphere models with longitudinal and latitudinal dependencies. We compare our model results with Io’s plasma environment measured with the instruments of the Galileo spacecraft during two Io passes: I24 and I27. We demonstrate that parts of the magnetic field perturbations, linked to the induction signals of a subsurface magma ocean (Khurana et al., 2011) can alternatively be explained by considering a global asymmetric atmosphere without considering induced fields from a subsurface magma ocean. Our analytic model results show that the resultant discontinuities for a plume that contains 50% of the mass content of Europa’s atmosphere would only contribute to about 5% for the magnetic field amplitudes generated by the global atmosphere. Furthermore we compare our model results with the measured magnetic field data from three flybys of the Galileo spacecraft at Europa which included Alfvén wing crossings: E17, E25A, and E26, to investigate if signals of plumes are visible in the magnetic field measurements. Our analysis suggests that the magnetic field perturbations measured along the E26 trajectory could be consistent with a plume on the southern hemisphere.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Blöcker, Aljona abloecker@web.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-77419
Date:	2017
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute for Geophysics and Meteorology
Subjects:	Physics Earth sciences
Uncontrolled Keywords:	Keywords Language Europa; Io; ocean; atmosphere; plumes; plasma interaction; induction; Galilean moons; Jupiter; magnetosphere English
Date of oral exam:	3 July 2017
Referee:	Name Academic Title Saur, Joachim Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/7741