Hydrogen Loss on Venus Driven by Photochemistry
Venus has experienced substantial H loss through hydrodynamic outflow in its early history, transforming from a warm and wet state to the current arid and scorching state. While Venus continues to lose H today, no consensus has been reached regarding the present dominant escape mechanisms. Recently,...
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2025-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/adec90 |
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| author | Hao Gu Jun Cui Xiaoshu Wu Xu Huang Shiqi Wu Wenlong Li Jinjin Zhao Haoyu Lu Lei Li |
| author_facet | Hao Gu Jun Cui Xiaoshu Wu Xu Huang Shiqi Wu Wenlong Li Jinjin Zhao Haoyu Lu Lei Li |
| author_sort | Hao Gu |
| collection | DOAJ |
| description | Venus has experienced substantial H loss through hydrodynamic outflow in its early history, transforming from a warm and wet state to the current arid and scorching state. While Venus continues to lose H today, no consensus has been reached regarding the present dominant escape mechanisms. Recently, photochemical escape via HCO ^+ dissociative recombination (DR) has been proposed as a prevailing process that had previously been overlooked. However, due to uncertainties in the underlying H _2 abundance and the solar cycle variations of the input radiative energy, it is essential to explore how these factors influence the modeled H escape flux under different conditions. By combining a photochemical model with a Monte Carlo test particle model, we demonstrate that the H escape flux increases with the underlying H _2 concentration over a possible range of 1 × 10 ^6 –2 × 10 ^8 cm ^−2 s ^−1 , but varies nonmonotonically with solar activity due to the competition between photochemical production and collisional hindrance. While our results confirm the dominant role of HCO ^+ DR, we find that the ion-neutral reaction ${\mathrm{OH}}^{+}+{\rm{O}}\to {{\rm{O}}}_{2}^{+}+{\rm{H}}$ makes an additional contribution, which could reach more than 30% of total H escape. Our findings provide valuable insights into the foundational understanding of photochemically driven H escape because the same mechanism should function in a much broader context. |
| format | Article |
| id | doaj-art-ddabcbbb1fb44509b7c4c6dcadebac41 |
| institution | DOAJ |
| issn | 2041-8205 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal Letters |
| spelling | doaj-art-ddabcbbb1fb44509b7c4c6dcadebac412025-08-20T03:12:49ZengIOP PublishingThe Astrophysical Journal Letters2041-82052025-01-019881L3110.3847/2041-8213/adec90Hydrogen Loss on Venus Driven by PhotochemistryHao Gu0https://orcid.org/0000-0002-9831-0618Jun Cui1https://orcid.org/0000-0002-4721-8184Xiaoshu Wu2https://orcid.org/0000-0003-4070-2050Xu Huang3https://orcid.org/0000-0003-0284-7689Shiqi Wu4Wenlong Li5https://orcid.org/0009-0009-9001-4724Jinjin Zhao6Haoyu Lu7https://orcid.org/0000-0002-2866-4736Lei Li8Planetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-Sen University , Zhuhai, Guangdong, People’s Republic of China ; cuijun7@mail.sysu.edu.cnPlanetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-Sen University , Zhuhai, Guangdong, People’s Republic of China ; cuijun7@mail.sysu.edu.cnPlanetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-Sen University , Zhuhai, Guangdong, People’s Republic of China ; cuijun7@mail.sysu.edu.cnPlanetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-Sen University , Zhuhai, Guangdong, People’s Republic of China ; cuijun7@mail.sysu.edu.cnPlanetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-Sen University , Zhuhai, Guangdong, People’s Republic of China ; cuijun7@mail.sysu.edu.cnPlanetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-Sen University , Zhuhai, Guangdong, People’s Republic of China ; cuijun7@mail.sysu.edu.cnPlanetary Environmental and Astrobiological Research Laboratory (PEARL), School of Atmospheric Sciences, Sun Yat-Sen University , Zhuhai, Guangdong, People’s Republic of China ; cuijun7@mail.sysu.edu.cnSchool of Space and Earth Sciences, Beihang University , Beijing, People’s Republic of ChinaNational Space Science Center, Chinese Academy of Sciences , Beijing, People’s Republic of ChinaVenus has experienced substantial H loss through hydrodynamic outflow in its early history, transforming from a warm and wet state to the current arid and scorching state. While Venus continues to lose H today, no consensus has been reached regarding the present dominant escape mechanisms. Recently, photochemical escape via HCO ^+ dissociative recombination (DR) has been proposed as a prevailing process that had previously been overlooked. However, due to uncertainties in the underlying H _2 abundance and the solar cycle variations of the input radiative energy, it is essential to explore how these factors influence the modeled H escape flux under different conditions. By combining a photochemical model with a Monte Carlo test particle model, we demonstrate that the H escape flux increases with the underlying H _2 concentration over a possible range of 1 × 10 ^6 –2 × 10 ^8 cm ^−2 s ^−1 , but varies nonmonotonically with solar activity due to the competition between photochemical production and collisional hindrance. While our results confirm the dominant role of HCO ^+ DR, we find that the ion-neutral reaction ${\mathrm{OH}}^{+}+{\rm{O}}\to {{\rm{O}}}_{2}^{+}+{\rm{H}}$ makes an additional contribution, which could reach more than 30% of total H escape. Our findings provide valuable insights into the foundational understanding of photochemically driven H escape because the same mechanism should function in a much broader context.https://doi.org/10.3847/2041-8213/adec90VenusPlanetary atmospheresAtmospheric evolutionUpper atmosphereSolar system terrestrial planets |
| spellingShingle | Hao Gu Jun Cui Xiaoshu Wu Xu Huang Shiqi Wu Wenlong Li Jinjin Zhao Haoyu Lu Lei Li Hydrogen Loss on Venus Driven by Photochemistry The Astrophysical Journal Letters Venus Planetary atmospheres Atmospheric evolution Upper atmosphere Solar system terrestrial planets |
| title | Hydrogen Loss on Venus Driven by Photochemistry |
| title_full | Hydrogen Loss on Venus Driven by Photochemistry |
| title_fullStr | Hydrogen Loss on Venus Driven by Photochemistry |
| title_full_unstemmed | Hydrogen Loss on Venus Driven by Photochemistry |
| title_short | Hydrogen Loss on Venus Driven by Photochemistry |
| title_sort | hydrogen loss on venus driven by photochemistry |
| topic | Venus Planetary atmospheres Atmospheric evolution Upper atmosphere Solar system terrestrial planets |
| url | https://doi.org/10.3847/2041-8213/adec90 |
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