近日，美国科罗拉多大学Chaffin, M. S.和Cangi, E. M.及其团队的研究揭示，金星失水主要是由HCO⁺解离复合引起的。这一研究成果于2024年5月6日发表在国际顶尖学术期刊《自然》上。

据研究人员介绍，尽管金星的大小和物质来源与地球相似，但它极其干燥，金星上几乎所有的水都流失到太空中去了，这是由于古老的、以蒸汽为主的大气中氢气的流出造成的。这种流体动力学逃逸可能移除了最初类似地球的3km全球等效层(GEL)的大部分水，但不能将大气消耗到观测到的3cm的GEL，因为它低于约10-100mGEL时关闭。为了使金星完全失水，并使观测到的大气氘含量达到地球的约120倍，需要至今仍在运行的非热氢逸出机制。早期的研究将其确定为共振电荷交换，热氧撞击和离子流出，建立了一个氢逃逸的共识观点，此后该观点只得到了很少的更新。

研究表明，这种共识忽略了当今最重要的氢损失过程，HCO⁺解离重组。这一过程几乎使金星H的逸出率增加了一倍，因此，维持稳定的大气水丰度所需的现今火山排气和/或撞击物降落量也翻了一番。这些较高的损失率解决了长期存在的难题，同时解释了金星水的测量丰度和同位素比率，并将使推测性晚期海洋情景之后的加速干燥成为可能。由于设计上的限制，过去的金星任务无法同时测量HCO⁺和由其重组产生的逸出氢。研究结果强调，未来的航天器测量势在必行。

附：英文原文

Title: Venus water loss is dominated by HCO⁺ dissociative recombination

Author: Chaffin, M. S., Cangi, E. M., Gregory, B. S., Yelle, R. V., Deighan, J., Elliott, R. D., Grller, H.

Issue&Volume: 2024-05-06

Abstract: Despite its Earth-like size and source material, Venus is extremely dry, indicating near-total water loss to space by means of hydrogen outflow from an ancient, steam-dominated atmosphere. Such hydrodynamic escape likely removed most of an initial Earth-like 3km global equivalent layer (GEL) of water but cannot deplete the atmosphere to the observed 3-cm GEL because it shuts down below about 10–100m GEL. To complete Venus water loss, and to produce the observed bulk atmospheric enrichment in deuterium of about 120times Earth, nonthermal H escape mechanisms still operating today are required. Early studies identified these as resonant charge exchange, hot oxygen impact and ion outflow, establishing a consensus view of H escape that has since received only minimal updates. Here we show that this consensus omits the most important present-day H loss process, HCO⁺ dissociative recombination. This process nearly doubles the Venus H escape rate and, consequently, doubles the amount of present-day volcanic water outgassing and/or impactor infall required to maintain a steady-state atmospheric water abundance. These higher loss rates resolve long-standing difficulties in simultaneously explaining the measured abundance and isotope ratio of Venusian water and would enable faster desiccation in the wake of speculative late ocean scenarios. Design limitations prevented past Venus missions from measuring both HCO⁺ and the escaping hydrogen produced by its recombination; future spacecraft measurements are imperative.

DOI: 10.1038/s41586-024-07261-y

Source: https://www.nature.com/articles/s41586-024-07261-y