H2 Chemistry and Protonation in the Dayside Venusian Upper Atmosphere
Although H _2 is present in low concentrations, it critically controls the structure and composition of planetary upper atmospheres through protonation under solar extreme-ultraviolet and soft X-ray irradiation. Recent studies highlight the importance of protonation on Venus. As H _2 concentrations...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astronomical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-3881/ad9d43 |
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| Summary: | Although H _2 is present in low concentrations, it critically controls the structure and composition of planetary upper atmospheres through protonation under solar extreme-ultraviolet and soft X-ray irradiation. Recent studies highlight the importance of protonation on Venus. As H _2 concentrations in its upper atmosphere remain poorly constrained, we conduct a systematic model investigation of how the structure of the topside Venusian ionosphere responds to varying H _2 distributions. Our model results suggest that protonated species could outnumber nonprotonated species in the topside ionosphere when ambient H _2 concentrations exceed 5 ppm. Generally, increasing H _2 concentrations enhances the degree of protonation, manifesting as elevated levels of most protonated species, while nonprotonated species are generally depleted due to rapid reactions with H _2 . These trends, however, are not universal; nonmonotonic variations among multiple species like OH ^+ and O ${}_{2}^{+}$ emerge, driven by the complex chemical network that intricately links species distributions throughout the upper atmosphere. The results presented here provide a foundation for improved characterization of hydrogen escape on Venus during its evolutionary history. |
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| ISSN: | 1538-3881 |