火星氘化电离层的完全耦合光化学及其对 H 和 D 逃逸的影响
Fully coupled photochemistry of the deuterated ionosphere of Mars and its effects on escape of H and D
AI总结：
本研究使用升级的完全耦合 1D 光化学模型探究火星氘化电离层，发现在所有太阳条件下非热逃逸主导原子 D 流失，总水分流失量达 147-158 m GEL，但仍低于地貌学估计。
摘要：
尽管火星上的氘（D）已受到广泛关注，但氘化电离层仍相对缺乏研究。这意味着我们对火星非热 D 逃逸也知之甚少，因为它主要由离子-中性反应中产生的原子所获得的过剩能量驱动。预计火星上大部分 D 逃逸是非热的，这凸显了我们对火星水分流失理解上的空白。在本研究中，我们着手填补这一知识空白。为实现目标，我们使用了一个升级的 1D 光化学模型，该模型完全耦合离子和中性物质，且不假设光化学平衡。据我们所知，此类模型此前未曾应用于火星。我们对太阳极小期、平均期和极大期的大气进行了建模，发现氘化电离层的行为与含 H 电离层相似，但在所有太阳条件下，量级为 8000-9000 cm$^{-2}$s$^{-1}$ 的非热逃逸主导了原子 D 的流失。总分馏因子 $f$ 为 $f=0.04$--0.07，累计水分流失量为 147--158 m GEL。这仍低于地貌学估计值。由于密度低以及与更丰富的 H 离子发生质量简并，火星上的氘化离子可能难以用现有技术测量。未来希望原位测量氘化电离层的任务将需要为此开发创新技术。
英文摘要：
Although deuterium (D) on Mars has received substantial attention, the deuterated ionosphere remains relatively unstudied. This means that we also know very little about non-thermal D escape from Mars, since it is primarily driven by excess energy imparted to atoms produced in ion-neutral reactions. Most D escape from Mars is expected to be non-thermal, highlighting a gap in our understanding of water loss from Mars. In this work, we set out to fill this knowledge gap. To accomplish our goals, we use an upgraded 1D photochemical model that fully couples ions and neutrals and does not assume photochemical equilibrium. To our knowledge, such a model has not been applied to Mars previously. We model the atmosphere during solar minimum, mean, and maximum, and find that the deuterated ionosphere behaves similarly to the H-bearing ionosphere, but that non-thermal escape on the order of 8000-9000 cm$^{-2}$s$^{-1}$ dominates atomic D loss under all solar conditions. The total fractionation factor, $f$, is $f=0.04$--0.07, and integrated water loss is 147--158 m GEL. This is still less than geomorphological estimates. Deuterated ions at Mars are likely difficult to measure with current techniques due to low densities and mass degeneracies with more abundant H ions. Future missions wishing to measure the deuterated ionosphere in situ will need to develop innovative techniques to do so.
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