Abstract The exosphere of Ganymede is the interface region linking the moon’s icy surface to Jupiter’s magnetospheric environment. Its characterization is of key importance to achieve a full understanding of the ice alteration processes induced by the radiation environment. Several scientific instruments that will operate on board the upcoming Jupiter Icy Moons Explorer (JUICE) mission, selected by ESA in the context of its Cosmic Vision programme, have the potential to study Ganymede’s exosphere. Among them, the Moons And Jupiter Imaging Spectrometer (MAJIS) will have the chance to investigate the composition of the moon’s exospheric components and the emission of water molecules. The exospheric water density profile, as obtained from current models, is a crucial parameter for the estimation of the expected signal to noise ratio related to the actual measurement. In lack of an adequate number of Ganymede’s observations from past missions, there is a general difficulty in constraining current exosphere models which are based, in general, on different scenarios and considerations and often show large discrepancies in the estimated spatial distribution of the neutral environment. In this work, we make a preliminary estimation of the expected IR emission from exospheric water molecules, using different modelled density profiles, and we speculate on the possibility of JUICE/MAJIS to detect it. An exercise on the potential plume detection capabilities of MAJIS is also performed. The first necessary step for performing these calculations is a rough comparison of the existing models of Ganymede’s water vapor exosphere. We discuss the characteristics of the neutral environment as derived from different exospheric models available in literature, the role of the ion-surface interactions in the H2O exosphere generation, and the related implications also in view of future observations. We then use the model outputs to estimate different scenarios for the expected non-Local Thermal Equilibrium (non-LTE) emission from these molecules. The results of this study can be of help during the JUICE observation planning phase.

中文翻译：

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MAJIS对木卫三水汽环境探测可能性的初步估计

摘要 木卫三外层是连接月球冰面与木星磁层环境的界面区域。其表征对于全面了解辐射环境引起的冰变化过程至关重要。欧洲航天局在其宇宙愿景计划的背景下选择了即将在即将到来的木星冰卫星探测器（JUICE）任务上运行的几种科学仪器，有可能研究木卫三的外逸层。其中，月球和木星成像光谱仪（MAJIS）将有机会研究月球外层成分的组成和水分子的发射。从当前模型获得的外层水密度分布，是估计与实际测量相关的预期信噪比的关键参数。由于缺乏足够数量的来自过去任务的木卫三观测，限制当前的外逸层模型普遍存在困难，这些模型通常基于不同的情景和考虑因素，并且在中性环境的估计空间分布中经常表现出很大的差异。在这项工作中，我们使用不同的建模密度剖面对外层水分子的预期红外发射进行了初步估计，并推测了 JUICE/MAJIS 检测到它的可能性。还对 MAJIS 的潜在羽流检测能力进行了练习。执行这些计算的第一个必要步骤是粗略比较木卫三的水蒸气外逸层的现有模型。我们讨论了从文献中可用的不同外逸层模型得出的中性环境的特征、离子表面相互作用在 H2O 外逸层生成中的作用，以及考虑到未来观察的相关影响。然后，我们使用模型输出来估计来自这些分子的预期非局部热平衡 (non-LTE) 发射的不同场景。这项研究的结果可以在 JUICE 观察计划阶段提供帮助。离子表面相互作用在 H2O 外逸层生成中的作用，以及考虑到未来观察的相关影响。然后，我们使用模型输出来估计来自这些分子的预期非局部热平衡 (non-LTE) 发射的不同场景。这项研究的结果可以在 JUICE 观察计划阶段提供帮助。离子表面相互作用在 H2O 外逸层生成中的作用，以及考虑到未来观察的相关影响。然后，我们使用模型输出来估计来自这些分子的预期非局部热平衡 (non-LTE) 发射的不同场景。这项研究的结果可以在 JUICE 观察计划阶段提供帮助。