Despite the numerous modeling efforts of the past, our knowledge on the radiation-induced physical and chemical processes in Europa’s tenuous atmosphere and on the exchange of material between the moon’s surface and Jupiter’s magnetosphere remains limited. In lack of an adequate number of in situ observations, the existence of a wide variety of models based on different scenarios and considerations has resulted in a fragmentary understanding of the interactions of the magnetospheric ion population with both the moon’s icy surface and neutral gas envelope. Models show large discrepancy in the source and loss rates of the different constituents as well as in the determination of the spatial distribution of the atmosphere and its variation with time. The existence of several models based on very different approaches highlights the need of a detailed comparison among them with the final goal of developing a unified model of Europa’s tenuous atmosphere. The availability to the science community of such a model could be of particular interest in view of the planning of the future mission observations (e.g., ESA’s JUpiter ICy moons Explorer (JUICE) mission, and NASA’s Europa Clipper mission). We review the existing models of Europa’s tenuous atmosphere and discuss each of their derived characteristics of the neutral environment. We also discuss discrepancies among different models and the assumptions of the plasma environment in the vicinity of Europa. A summary of the existing observations of both the neutral and the plasma environments at Europa is also presented. The characteristics of a global unified model of the tenuous atmosphere are, then, discussed. Finally, we identify needed future experimental work in laboratories and propose some suitable observation strategies for upcoming missions.

中文翻译：

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迈向欧罗巴脆弱大气的全球统一模型

尽管过去进行了大量建模工作，但我们对木卫二稀薄大气中辐射引起的物理和化学过程以及月球表面与木星磁层之间的物质交换的了解仍然有限。由于缺乏足够数量的原位观测，基于不同情景和考虑的多种模型的存在导致对磁层离子群与月球冰面和中性气体包层的相互作用的理解不完整。模型显示不同成分的来源和损失率以及大气空间分布及其随时间变化的确定存在很大差异。基于不同方法的几种模型的存在凸显了对它们进行详细比较的必要性，最终目标是开发木卫二脆弱大气的统一模型。考虑到未来任务观测的规划（例如，欧空局的木星冰冷卫星探索者 (JUICE) 任务和美国宇航局的欧罗巴快船任务），科学界对这种模型的可用性可能特别感兴趣。我们回顾了木卫二稀薄大气的现有模型，并讨论了它们中性环境的每个派生特征。我们还讨论了不同模型之间的差异以及木卫二附近等离子体环境的假设。还介绍了对欧罗巴中性环境和等离子体环境的现有观察结果的摘要。然后讨论了稀薄大气的全球统一模型的特征。最后，我们确定了实验室未来所需的实验工作，并为即将到来的任务提出了一些合适的观测策略。