Optical Properties of Venusian Clouds

摘要：尽管经过多年的研究，金星的大气层仍未得到很好的了解。当检查来自金星大气层的光谱时，在大约320 -500nm处存在一个尚未解释的吸收区域（p<s:1> rez- hoyos等人，2018）。这对应于光谱中的蓝色至紫外线区域，或“近紫外线”，尽管不同作者引用的确切范围不同（例如参见Pollack等人，1980;Frandsen, Wennberg, & Kjaergaard, 2016；Ekonomov等人，1984；Limaye等人，2019）。这种吸收被认为发生在金星的上层云层，由h2so4 /H2O混合物组成的液滴。这种吸收不能仅仅用液滴或SO2气体的夹杂来解释，因此有人提出在液滴或气体中混入一种额外的微粒或气溶胶吸收剂（Ekonomov et al., 1984; Pollack et al., 1980）。虽然已经提出了几种候选物质，但没有一种化学物质被最终证明符合观察到的金星的吸收模式和大气化学。本项目将研究含有候选吸收剂的硫酸液滴的光学性质。这将首先在散装液体或气溶胶分布中进行，然后使用光学镊子在单个液滴中进行。该项目还将考虑液滴中吸收剂候选材料的物理和更一般的光学特性，包括实际折射率和保持球形的能力。在金星上观测到的光荣图案——当光线在内部反射时，在球形水滴中产生的一系列同心彩色光圈（Laven, 2005）。观察到的光晕表明液滴中存在吸收剂颗粒。颗粒必须完全在液滴内，因为将颗粒附着在液滴表面会导致光晕的扭曲，而这是无法观察到的。一些候选材料不可能插入液滴中，因此，无论它们与检测到的光学性质和吸收率是否一致，都不能成为吸收剂（Petrova, 2018）。LMD （Le Laboratoire de msamtsamorologie Dynamique）金星大气模式全面模拟了金星的云层。从实验室实验中得到的有希望的候选者的物理、化学和光学性质可以包括在模型中，以模拟它们在金星大气中的行为，从而检查它们作为候选者的适用性。除了有助于缩小搜索范围或加强识别吸收剂的证据外，在模型中纳入已确认的吸收剂将提高其模拟现实行为以解决其他问题的能力。如果没有一种候选者似乎足以提供所检测到的全部吸收，计算机模拟将特别有用。然后利用模型将候选吸收剂以不同的数量和配对组合起来，看看是否有任何有希望的吸收剂。如果预测到有希望的候选混合物，则可以开始对混合物进行实验测试，并且可以迭代地进行该过程以确定吸收剂比率。

Abstract: Despite many years of study, the atmosphere of Venus is not well understood. When the spectrum of light from Venus's atmosphere is examined, there is an as yet unexplained region of absorption at approximately320 -500nm (Pérez-Hoyos et al., 2018). This corresponds to the blue to ultraviolet region of the spectrum, or "near-UV", although the exact range is quoted differently by different authors, (see for example Pollack et al., 1980;Frandsen, Wennberg, & Kjaergaard, 2016;Ekonomov et al., 1984;Limaye et al., 2019).The absorption is believed to occur in the upper cloud layer of Venus, which consists of droplets of anH2SO4/H2O mixture. The absorption cannot be explained by the droplets alone, or by the inclusion of SO2 gas, and so an additional particulate or aerosol absorber mixed in with the droplets or gas has been proposed (Ekonomov et al., 1984; Pollack et al., 1980).Although several candidates have been suggested, no chemical species has been conclusively proven to fit the observed absorption pattern and atmospheric chemistry of Venus. This project will examine the optical properties of sulphuric acid droplets containing candidate absorbers. This will be done initially in bulk liquid or aerosol distributions, and then in single droplets using optical tweezers. The project will also consider the physical and more general optical properties of the absorber candidates in droplets, including real refractive index and ability to maintain a spherical shape. Glory patterns -a series of concentric coloured rings of light produced in spherical droplets when light is internally reflected (Laven, 2005)-have been observed on Venus. The observed glories suggest the presence of absorber particles in the droplets. The particles must be entirely within the droplets as attaching particles to the droplet surface would result in distortion of the glory, which is not observed. Some candidates are impossible to insert into droplets and so, regardless of their agreement with the optical properties and absorption detected, cannot be the absorber (Petrova, 2018).The LMD (Le Laboratoire de Météorologie Dynamique) Venus atmosphere model comprehensively models the clouds of Venus. The physical, chemical, and optical properties of promising candidates from the laboratory experiments can be included in the model to simulate their behaviour in the Venusian atmosphere and therefore to check their suitability as candidates. As well as helping narrow down the search or strengthening the evidence for the identification of the absorber, the inclusion of a confirmed absorber in the model will improve its ability to model realistic behaviour to solve other problems.Computer modelling will be particularly useful if no single candidate seems sufficient to provide all of the absorption detected. Modelling would then be used to combine candidate absorbers in variable amounts and pairings to see if any are promising. If promising candidate mixtures are predicted, experimental tests of the mixtures could begin, and the process could proceed iteratively to identify the absorber ratios.