• ISSN 2097-1893
  • CN 10-1855/P

类地天体外逸层及其变化性研究进展

Research progress on the exosphere and its variability of terrestrial bodies

  • 摘要: 外逸层是类地天体大气的重要组成部分,其结构与变化性对理解行星物质流失、大气的演化及行星宜居性具有重要科学意义. 本文系统回顾了近 60 年来类地天体外逸层的研究进展,涵盖其形成机制、观测与模拟方法以及变化性. 从起源上看,外逸层可分为三种类型:低层大气起源外逸层、表面起源外逸层和内部起源外逸层. 外逸层粒子在形成后还会经历多种损失过程,使其结构始终处于动态演化之中. 光谱观测和质谱探测是研究外逸层的主要观测手段,为解析外逸层结构与变化性提供了重要基础. 经典 Chamberlain 模型是最广泛应用于解析外逸层密度分布的方法. 随后提出的 Boltzmann 传输方程和Monte Carlo 模拟则进一步考虑了逃逸面以下粒子增能过程的影响,特别在研究局部热平衡偏离和高能非热成分逃逸方面具有优势. 外逸层的变化性受到内外部多种因素的共同作用,包括太阳活动周期变化、耀斑事件、低层大气物理和动力学过程及双星系统中的引力相互作用等外部因素,以及天体内部活动等内部因素. 这些因素通过影响外逸层粒子的生成与损失,显著改变其结构特征. 本文通过梳理相关研究成果,旨在为未来进一步完善外逸层形成理论、揭示其动力学特性及探究其对行星大气演化和宜居性影响提供重要参考.

     

    Abstract: Exosphere is an essential component of the atmospheres of terrestrial bodies. Its structure and variability hold significant scientific values for understanding planetary material loss, atmospheric evolution, and habitability. This paper systematically reviews the progress in the study of the exospheres of terrestrial bodies over the past 60 years, covering their formation mechanisms, observational and simulation methods, and variabilities. In terms of origin, the exospheres can be classified into three types: lower atmosphere-origin exospheres, surface-origin exospheres, and interior-driven exospheres. After their formations, exospheric particles also undergo various loss processes, keeping the structures of the exospheres in a state of dynamic evolution. Spectroscopic and mass spectrometric measurements are the primary observational methods for studying exospheres, providing essential data for analyzing their structures and variabilities. The classical Chamberlain model remains the most widely used approach for deriving exospheric density distributions. Subsequent developments, including the Boltzmann transport equation and Monte Carlo simulations, further incorporate the effects of particle energization below the exobase, making them particularly advantageous for studying deviations from local thermodynamic equilibrium and the escape of high-energy non-thermal particles. The variabilities of the exospheres are driven by both internal and external factors, including external drivers such as solar cycle, solar flares, physical and dynamical processes in the lower atmosphere, and gravitational interactions in binary systems, as well as internal processes such as geological activities. These factors significantly alter the structural characteristics of the exospheres by affecting the generation and loss of exospheric particles. By reviewing relevant research findings, this paper aims to provide valuable references for further improving the theoretical framework of exosphere formation, elucidating its dynamic properties, and investigating its impact on planetary atmospheric evolution and habitability.

     

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