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Register a new userSources of Pressure in Titans Plasma Environment
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N. Achilleos
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In order to analyze varying plasma conditions upstream of Titan, we have combined a physical model of Saturns plasmadisk with a geometrical model of the oscillating current sheet. During modeled oscillation phases where Titan is furthest from the current sheet, the main sources of plasma pressure in the near-Titan space are the magnetic pressure and, for disturbed conditions, the hot plasma pressure. When Titan is at the center of the sheet, the main source is the dynamic pressure associated with Saturns cold, subcorotating plasma. Total pressure at Titan (dynamic plus thermal plus magnetic) typically increases by a factor of five as the current sheet center is approached. The predicted incident plasma flow direction deviates from the orbital plane of Titan by < 10 deg. These results suggest a correlation between the location of magnetic pressure maxima and the oscillation phase of the plasmasheet.
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Numerous geological features that could be evaporitic in origin have been identified on the surface of Titan. Although they seem to be water-ice poor, their main properties -chemical composition, thickness, stratification- are essentially unknown. In this paper, which follows on a previous one focusing on the surface composition (Cordier et al., 2013), we provide some answers to these questions derived from a new model. This model, based on the up-to-date thermodynamic theory known as PC-SAFT, has been validated with available laboratory measurements and specifically developed for our purpose. 1-D models confirm the possibility of an acetylene and/or butane enriched central layer of evaporitic deposit. The estimated thickness of this acetylene-butane layer could explain the strong RADAR brightness of the evaporites. The 2-D computations indicate an accumulation of poorly soluble species at the deposits margin. Among these species, HCN or aerosols similar to tholins could play a dominant role. Our model predicts the existence of chemically trimodal bathtub rings which is consistent with what it is observed at the south polar lake Ontario Lacus. This work also provides plausible explanations to the lack of evaporites in the south polar region and to the high radar reflectivity of dry lakebeds.
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