Abstract The future Europa Clipper NASA mission to Europa will carry the MAss Spectrometer for Planetary EXploration (MASPEX), which will analyze the compounds making up Europa’s exosphere, and plumes, if present. Europa’s exosphere is likely to feature abundant atomic oxygen, a product of sputtering of Europa’s surface by energetic particles from Jupiter’s radiation belts, or photolysis of oxygen-bearing molecules in the exosphere. Due to its very high reactivity, this atomic oxygen could induce chemical processes within MASPEX. These processes could involve materials composing the instrument, or other compounds from Europa’s exosphere. In both cases, the possible effect on the instrument’s measurements is a concern. In this work we first review previous relevant experiments on the effect of atomic oxygen on several candidate metals and conclude that stainless steel with a gold coating is the most satisfactory choice for MASPEX’s antechamber walls, and alumina for the impact plate. We then perform simulations of adsorption/desorption processes within the instrument’s antechamber to bound the effect of atomic oxygen on other compounds from Europa’s exosphere. We find that the accumulation of atomic oxygen during a flyby would lead to a reduction of the apparent abundance of water by as much as 0.125% (Δ[H2O]/[H2O] ​= ​−1.25 ​× ​10−3). Evaluating the exact extent of this effect during data post-processing would require constraining the atomic oxygen abundance, which would have to be achieved with other instruments, such as the ultraviolet spectrometer.

中文翻译：

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木卫二外逸层的原子氧对行星探测质谱仪的预期影响

摘要 未来的欧罗巴快船 NASA 前往欧罗巴的任务将携带用于行星探索的质谱仪 (MASPEX)，它将分析构成欧罗巴外逸层和羽流（如果存在）的化合物。木卫二的外逸层很可能具有丰富的原子氧，这是木星辐射带的高能粒子在木卫二表面溅射的产物，或外逸层中含氧分子的光解作用。由于其非常高的反应性，这种原子氧可以在 MASPEX 中引发化学过程。这些过程可能涉及构成仪器的材料，或来自木卫二外逸层的其他化合物。在这两种情况下，对仪器测量的可能影响是一个问题。在这项工作中，我们首先回顾了先前关于原子氧对几种候选金属的影响的相关实验，并得出结论，带有金涂层的不锈钢是 MASPEX 前室壁的最令人满意的选择，而撞击板是氧化铝。然后，我们在仪器的前室内进行吸附/解吸过程的模拟，以限制原子氧对木卫二外逸层其他化合物的影响。我们发现飞越过程中原子氧的积累会导致水的表观丰度减少多达 0.125% (Δ[H2O]/[H2O] = -1.25 × 10-3)。在数据后处理期间评估这种影响的确切程度需要限制原子氧丰度，而这必须通过其他仪器（例如紫外光谱仪）来实现。