Recent Mars Atmosphere and Volatile EvolutioN (MAVEN) observations have shown unexpectedly large deuterium Lyman‐α emissions near the Martian southern summer solstice. The deuterium Lyman‐α brightness can reach ∼10% of the hydrogen Lyman‐α brightness below 200 km. In this study, we propose a method to estimate the D/H ratio in the Martian upper atmosphere through analysis of the Lyman‐α vertical profiles without the ability to spectrally separate the two atomic emission lines. Lyman‐α vertical profiles measured by MAVEN/IUVS at four periods are analyzed. During southern summer, the derived D/H ratios at 200 km are larger than the HDO/H₂O ratio measured in the lower atmosphere, yet the extrapolated D/H ratio from 200 to 80 km agrees with the HDO/H₂O ratio. This larger D/H ratio at higher altitude is attributed to the more efficient escape of hydrogen atoms compared to deuterium atoms. The method we describe accounts for uncertainties related to constraining the temperature and density profiles of H and D in the lower thermosphere. Because spectrally resolved D and H Lyman‐α measurements are not always available, this method provides a way to estimate D/H variations in their absence. This method will be useful for analysis of relevant data sets from past and future Mars missions.

中文翻译：

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利用MAVEN / IUVS的低光谱分辨率模式估算火星高层大气的D / H比

最近的火星大气和挥发份观测（MAVEN）观测表明，火星南部夏至附近的氘Lyman-α排放量出乎意料。在200 km以下，氘的Lyman-α亮度可以达到氢Lyman-α亮度的约10％。在这项研究中，我们提出了一种通过分析Lyman-α垂直剖面来估算火星高空大气层中D / H比的方法，该方法无法光谱分离两条原子发射线。分析了通过MAVEN / IUVS在四个周期内测得的Lyman-α垂直剖面。在南部夏季，在200 km处得出的D / H比值大于在低层大气中测得的HDO / H ₂ O比值，但从200至80 km推算出的D / H比值与HDO / H _2值一致O比率。与氘原子相比，在更高的高度处更大的D / H比归因于氢原子更有效的逸出。我们描述的方法考虑了与限制较低热圈中H和D的温度和密度分布有关的不确定性。由于光谱分辨的D和HLyman-α测量并非始终可用，因此该方法提供了一种在不存在D / H变化的情况下估计其变化的方法。该方法对于分析过去和将来的火星飞行任务的相关数据集很有用。