Hybrid simulations of the plasma environment around Enceladus

作者：Omidi N^*; Russell C T; Tokar R L; Leisner J S

来源：Journal of Geophysical Research, 2010, 115: A05212.

DOI：10.1029/2009JA014391

The plasma environment around Enceladus is governed by the interaction between the corotating plasma with the body of the moon and the neutral gas associated with Saturn's extended cloud and plumes ejected from its southern polar region. To understand the nature of this interaction, we use 3-D electromagnetic hybrid simulations that treat ions kinetically through particle-in-cell methods and treat the electrons as a charge-neutralizing fluid. In these simulations, plasma interaction with the neutrals takes place through charge exchange. The results show that plasma absorption by Enceladus forms a tail-like density cavity behind the moon and a depletion wake which is confined in the direction perpendicular to the magnetic field but extends many Enceladus radii along the magnetic field. Except in the cavity tail, the flow is not slowed by the interaction but is diverted toward the cavity in a symmetric fashion. Interaction of the corotating plasma with the extended neutrals results in the generation of ion cyclotron waves and plasma deceleration to velocities below the corotation speed. The results also show that the extent to which the presence of a plume in the southern pole affects the nature of the interaction depends on its density. For plumes with base densities of similar to 10(6)/cm(3) (6.5 x 10(29) molecules in the plume) or lower we find no significant impacts, while plumes with base densities of similar to 10(7)/cm(3) and larger are found to greatly impact the interaction region. Specifically, the interaction is no longer symmetric with a density cavity tail in the Northern Hemisphere and a density enhancement tail in the Southern Hemisphere. At base densities of similar to 10(8)/cm(3), a strong Alfven wing is also generated in the interaction. Preliminary comparisons of the simulations with the Cassini Plasma Spectrometer data during the 12 March 2008 encounter with Enceladus suggest plume base densities of similar to 5 x 10(8)/cm(3) corresponding to production of similar to 4 kg/s of new ions.

• 出版日期2010-5-19