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M. L. Marconi (Fresh Pond Research)
Gas tori are generated when escaping gases from planetary satellites organize themselves about the central planet. They are quite common in our solar system and are likely to be common in other solar systems. It is conceivable that extrasolar planetary atmospheres will be detected first from the emissions of their associated gas tori. It is, therefore, of considerable interest to understand their basic properties. Examples of gas tori in our solar system include the Io neutral clouds and the Titan hydrogen torus. These are examples of collisionless gas tori and have been studied extensively by various investigators. Other gas tori, for example, the Triton tori and possibly some gas tori in the inner Saturnian system (within 10 Saturn radii) are quasi-collisional, i.e., self-collision(torus particle-torus particle collisions) time above orbital period and below loss time(Smyth and Marconi Icarus, 101, 18, 1993). This type of quasi-collisonal tori is significantly more difficult to calculate, requiring the solution of the nonlinear Boltzmann equation. The only example of such a calculation is apparently by Decker and Chang (JGR,99,1994) in the context of interpretating the Voyager 2 PLS data from the Neptunian magnetosphere. We have recently begun a systematic study of the Triton H, N ,and H2 quasi-collisional tori in the Neptune system. A multispecies axisymmetric kinetic DSMC (direct Simulation Monte Carlo)model has been developed and has been applied to an H torus as well as an H and N torus. We present results for structure and evolution and for varying source properties (velocity distribution and flux at Triton's exobase) and discuss the effect of solar radiation and plasma chemistry. This work is supported by the NSF Astronomy Program.
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