Kinetic simulation of the distribution and escape of minor components of Titan's exosphere

Possessing the most significant atmosphere among icy satellites in Saturnian system, Titan attracts attention as a source of material in the Saturnian magnetosphere and makes the problem of understanding the distribution and escape of neutral components from its exosphere both interesting and important. Modeling of the neutral gas distribution throughout the exosphere is complicated because of the dramatic variation of its density. The collision regime of the gas flow in the exosphere starts as collision dominated at the boundary with a lower part of the atmosphere, where the gas is successfully described with its density, bulk velocity and temperature and becomes free molecular flow somewhat above the exobase, where momentum exchange between molecules has a negligible effect. In this case, adoptation of a kinetic approach is required for both the simulation of suprathermal components of the exosphere and possibly to correctly understand the structure of the exobase region itself. The presented work is aimed at the development of a kinetic numerical model that would be suitable for studying properties of suprathermal neutral components of upper planetary atmospheres, where the collision frequency is such that the validity of a fluid approach is limited. The model is applied to a case of the upper atmosphere of Titan in order to study distribution and escape of neutrals from its exosphere, the return flux to the lower atmosphere and influence of heating sources on neutrals distribution and ionization rate at the exosphere.