An approach to numerical simulation of the gas distribution in the atmosphere of Enceladus
Abstract
In addition to being the major source of neutral gas and dust particles for the Saturnian E-ring and, ultimately, heavy ions for the Saturnian inner magnetosphere, Enceladus exhibits geological activity that has made it an object of recent intensive study. The interest has significantly increased after Cassini flybys in 2005 provided a detailed map of its surface, showing that most of activity occurs in a region around the south pole of the satellite. During Cassini measurements of the atmosphere of Enceladus performed during 2005-2010, a large amount of information was collected on the atmospheric chemical composition along flyby trajectories as well as column densities of gas in the atmosphere obtained with occultation measurements. Dust jets that were discovered during the flybys can be related to a set of localized gas sources that dominates the supply of material into the rarefied atmosphere of Enceladus. In this paper we present two models of the atmosphere of Enceladus to explain the data collected with the Ultraviolet Imaging Spectrograph (UVIS) [Hansen et al., 2006] and the Ion and Neutral Mass Spectrometer (INMS) [Waite et al., 2006] instruments. Our multi-plume semi-analytical model was used to determine parameters of Enceladus' gas production by fitting INMS and UVIS data. The basic physical assumption of the model is splitting the total gas source in the atmosphere among a uniform source and eight point sources located at origins of the observed jets. Expansion of a gas from a point source can be described analytically by solving the Liouville equation. The most important force that governs motion of gas molecules outside of a vent is the gravity of Enceladus. The analytical approach for the density distribution cannot account for the gravity because it will destroy the axial symmetry of a jet implicitly embedded into the multi-plume model. A test particle Monte-Carlo model is used to check the importance of Enceladus' gravity in determining the density distribution within its atmosphere. The principal difference of the models presented here from those developed by other authors [Jurac et al., 2002; Waite et al., 2006; Burger et al., 2007; Tian et al., 2007; Matson et al., 2007] is a fully three-dimensional treatment of the atmosphere that allows us to include a set of gas sources located at the points of origin of the observed jets [Porco et al., 2006; Spitale and Porco, 2007]. Presented results include an analysis of recent E7 INMS data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.P23C..10T
- Keywords:
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- 6280 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS / Saturnian satellites