Gas flow and dust acceleration in a cometary Knudsen layer

被引:39
作者
Skorov, YV
Rickman, H
机构
[1] MV Keldysh Appl Math Inst, Moscow 125047, Russia
[2] Max Planck Inst Aeron, D-37191 K Lindau, Germany
[3] Astron Observ, S-75120 Uppsala, Sweden
关键词
D O I
10.1016/S0032-0633(99)00008-2
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
An analytical model of the innermost gas-dust coma region is proposed. The kinetic Knudsen layer adjacent to the surface of the cometary nucleus, where the initially non-equilibrium velocity distribution function of gas molecules relaxes to Maxwell equilibrium distribution function and, as a result, the macro-characteristics of gas and dust flows vary several-fold, is considered. The gas phase model is based on the equations for mass, momentum and energy flux conservation, and is a natural development of the Anisimov (1968) and Cercignani (1981) approaches. The analytical relations between the characteristics of the gas flow on the boundaries of the non-equilibrium layer and the characteristics of the returning gas flow adsorbed by the surface are determined. These values form a consistent basis both for hydrodynamic models of the inner coma and for jet force models. Three particular models are presented: (1) sublimation of a polyatomic one-component gas; (2) sublimation of a two-component polyatomic gas mixture, in both cases from a plane surface; and (3) sublimation of water ice through a porous dust mantle. We conclude that the characteristics of the gas flow emerging from the Knudsen layer over a porous dust mantle is not very sensitive to the structure of the mantle. We also treat the expansion of dust into the coma, concentrating on the interaction between a non-equilibrium gas flow and a test particle. The dynamics of a grain of idealized shape is explored by using several simplifying assumptions for the variation of the drag force. The velocity of a particle at the exterior boundary of the Knudsen layer is thus estimated. Examining various model behaviours of the drag force inside the Knudsen layer, we show that the dust velocity is not sensitive to these variations. (C) 1999 Elsevier Science Ltd. All rights reserved.
引用
收藏
页码:935 / 949
页数:15
相关论文
共 22 条
[1]  
ANISIMOV SI, 1968, ZH EKSP TEOR FIZ, V54, P339
[2]  
[Anonymous], ESA C P
[3]  
Baines M. J., 1965, Mon. Not. R. Astron. Soc., V130, P63, DOI [10.1093/mnras/130.1.63, DOI 10.1093/MNRAS/130.1.63]
[4]   A MODEL FOR COLLISION PROCESSES IN GASES .1. SMALL AMPLITUDE PROCESSES IN CHARGED AND NEUTRAL ONE-COMPONENT SYSTEMS [J].
BHATNAGAR, PL ;
GROSS, EP ;
KROOK, M .
PHYSICAL REVIEW, 1954, 94 (03) :511-525
[5]  
Bird G.A., 1976, MOL GAS DYNAMICS
[6]  
Cercignani C., 1981, Prog. Astronaut. Aeronaut, V74, P305
[7]  
CRIFO JF, 1987, ASTRON ASTROPHYS, V187, P438
[8]   The dependence of the circumnuclear coma structure on the properties of the nucleus .2. First investigation of the coma surrounding a homogeneous, aspherical nucleus [J].
Crifo, JF ;
Rodionov, AV .
ICARUS, 1997, 129 (01) :72-93
[9]  
CROVISIER J, 1984, ASTRON ASTROPHYS, V130, P361
[10]  
CROVISIER J, 1993, ASTEROIDS COMETS MET, P313