Global Venus‐Solar Wind Coupling and Oxygen Ion Escape. Issue 3 (9th February 2021)

• Record Type: Journal Article
• Authors: Persson, M.; Futaana, Y.; Ramstad, R.; Schillings, A.; Masunaga, K.; Nilsson, H.; Fedorov, A.; Barabash, S.
• Is Part Of: Geophysical research letters. Volume 48:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-02-09
• Subjects: atmospheric evolution -- ion escape -- solar wind -- Venus -- water; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL091213
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The present‐day Venusian atmosphere is dry, yet, in its earlier history a significant amount of water evidently existed. One important water loss process comes from the energy and momentum transfer from the solar wind to the atmospheric particles. Here, we used measurements from the Ion Mass Analyzer onboard Venus Express to derive a relation between the power in the upstream solar wind and the power leaving the atmosphere through oxygen ion escape in the Venusian magnetotail. We find that on average 0.01% of the available power is transferred, and that the percentage decreases as the available energy increases. For Mars the trend is similar, but the efficiency is higher. At Earth, the ion escape does not behave similarly, as the ion escape only increases after a threshold in the available energy is reached. These results indicate that the Venusian induced magnetosphere efficiently screens the atmosphere from the solar wind. Plain Language Summary: Today, there is barely any water on Venus, but presumably a large amount existed in its earlier history. Therefore, the water must have been lost over the course of the Venusian history. An important process for removal of water is escape to space, induced by the interaction between the Venusian atmosphere and the solar wind (a fast stream of particles ejected from the Sun). In this study, we investigated the connection between the energy available in the upstream solar wind and the energy leaving Venus in the form of oxygen ion escape. By characterizing this relation, we investigate how the Venusian atmosphere reacts to changes in the upstream solar wind and how well it protects itself from atmospheric loss caused by the solar wind. We find that the energy transfer decreases as the available upstream energy increases, a trend that is very similar to that found at Mars. However, the Venusian atmosphere seems to absorb less energy from the solar wind than Mars. This indicates that the Venusian induced magnetosphere efficiently screens the atmosphere from the solar wind. This is important for the understanding of the effect of the solar wind on the Venusian atmospheric evolution. Key Points: The total escaping power from Venus does not increase linearly with increasing available power in the solar wind The coupling coefficient, that is, ratio between power out and in, decreases with increasing solar wind energy flux The trend of the coupling coefficient with the upstream parameters for Venus is similar to that of Mars but different from that of Earth