A KINETIC-MODEL OF GAS-FLOW IN A POROUS COMETARY MANTLE

A numerical study of ags flow through a porous cometary mantle is pres ented. A kinetic model based on the well-known Test Particle Monte Car lo Method for the solution of rarefied gas dynamics problems is propos ed. The physical model consists of two spatial plane regions: the cond ensed ice phase and porous dust mantle. The structure of the porous du st layer is described as a bundle of cylindrical inclined channels not crossing each other. A vertical temperature gradient may exist across the dust mantle. The aim is to investigate how the characteristics of molecular flow depend on the capillary length, inclination angle, and temperature gradient. Examples illustrating a significant deviation o f some results from equilibrium values are shown. In particular, the g as velocity distribution at both ends of the pore is strongly non-Maxw ellian if there is an important temperature contrast across the pore. The emergent gas flow rate is found to vary with the pore length/radiu s ratio in excellent agreement with Clausing's empirical formula. The degree of collimation of the flow is quantitatively studied as a funct ion of the length/radius ratio, and consequences for the jet force of outgassing through a dust mantle or, indeed, a rough surface are estim ated.