土星环状大气结构研究

巨行星通常拥有独特的环状大气结构（toroidal atmospheres）。巨行星卫星的大气逃逸构成环状大气粒子的"源"，而与巨行星磁层等离子体之间的相互作用构成环状大气粒子的"汇"，因而对环状大气的研究是认识卫星大气逃逸机制和巨行星磁层等离子体分布的一个有效手段。本项目拟在蒙特卡罗粒子动力学的框架下，建立自洽的巨行星环状大气结构模型，既包括无碰撞条件下的测试粒子蒙特卡洛模型，也包括考虑环状大气粒子自碰撞的直接模拟蒙特卡洛模型。模型将结合Cassini质谱仪就位探测数据，用于计算土星环状大气各种成分（H、O、N、H2、N2、CH4、CH3、H2O和OH等）的密度分布，并研究环状大气结构如何受卫星大气逃逸及土星磁层等离子体分布的调制。本项目的提出符合我国深空探测和行星科学发展的需求。

Giant planets contain a unique type of atmospheres with toroidal appearance. Atmospheric escape from the natural satellites of giant planets serves as the source while the interaction with ambient magnetospheric plasma serves as the sink. Studying toroidal atmospheres thus provides an efficient way for probing the escape mechanisms occurring on satellites and the plasma environment corotating around giant planets. This project is aimed at constructing a Monte-Carlo molecular dynamical model that could be used to characterize the structures of toroidal atmospheres in a self-consistent manner, including both test particle Monte Carlo in the collisionless domain and direct simulation Monte Carlo that takes into account self-collisions between torus particles. Combined with in-situ measurements made with the mass spectrometer onboard Cassini, the model will be applied to various components of Saturn's toroidal atmosphere including H, O, N, H2, N2, CH4, CH3, H2O and OH. The modulation of the structure of the toroidal atmosphere by atmospheric escape from satellites as well as the plasma distribution in Saturn's magnetosphere will also be investigated. The implementation of this project fully matches China's long-term deep space exploration and the associated advancement of planetary sciences.