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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 26, issue 3
Ann. Geophys., 26, 619–637, 2008
https://doi.org/10.5194/angeo-26-619-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 26, 619–637, 2008
https://doi.org/10.5194/angeo-26-619-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  26 Mar 2008

26 Mar 2008

Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data

E. Roussos1, J. Müller2, S. Simon2, A. Bößwetter2, U. Motschmann2, N. Krupp1, M. Fränz1, J. Woch1, K. K. Khurana3, and M. K. Dougherty4 E. Roussos et al.
  • 1Max Planck Institut für Sonnensystemforschung, Max Planck Str. 2, 37191, Katlenburg-Lindau, Germany
  • 2Institut für Theoretische Physik, TU Braunschweig, Germany
  • 3Institute of Geophysics and Planetary Physics, University of California at Los Angeles, USA
  • 4Blackett Laboratory, Imperial College London, UK

Abstract. Rhea's magnetospheric interaction is simulated using a three-dimensional, hybrid plasma simulation code, where ions are treated as particles and electrons as a massless, charge-neutralizing fluid. In consistency with Cassini observations, Rhea is modeled as a plasma absorbing obstacle. This leads to the formation of a plasma wake (cavity) behind the moon. We find that this cavity expands with the ion sound speed along the magnetic field lines, resulting in an extended depletion region north and south of the moon, just a few Rhea radii (RRh) downstream. This is a direct consequence of the comparable thermal and bulk plasma velocities at Rhea. Perpendicular to the magnetic field lines the wake's extension is constrained by the magnetic field. A magnetic field compression in the wake and the rarefaction in the wake sides is also observed in our results. This configuration reproduces well the signature in the Cassini magnetometer data, acquired during the close flyby to Rhea on November 2005. Almost all plasma and field parameters show an asymmetric distribution along the plane where the corotational electric field is contained. A diamagnetic current system is found running parallel to the wake boundaries. The presence of this current system shows a direct corelation with the magnetic field configuration downstream of Rhea, while the resulting j×B forces on the ions are responsible for the asymmetric structures seen in the velocity and electric field vector fields in the equatorial plane. As Rhea is one of the many plasma absorbing moons of Saturn, we expect that this case study should be relevant for most lunar-type interactions at Saturn.

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