Optical Properties of Venusian Clouds

摘要：尽管进行了多年的研究，但人们对金星的大气层还没有很好的了解。当检查来自金星大气的光的光谱时，在大约320-500纳米处有一个尚未解释的吸收区域(Pérez-Hoyos等人，2018)。这对应于光谱的蓝色到紫外线区域，或“近紫外线”，尽管不同的作者引用了不同的确切范围(例如，见Pollack等人，1980年；Frandsen，Wennberg和Kjairgaard，2016；Ekonomov等人，1984；Limaye等人，2019年)。吸收被认为发生在金星的上层云层，它由H_2SO_4/H_2O混合物的液滴组成。这种吸收不能用液滴本身或SO2气体的包裹体来解释，因此提出了一种与液滴或气体混合的额外的颗粒或气溶胶吸收器(Ekonomov等人，1984；波拉克等人，1980)。尽管已经提出了几个候选方案，但没有任何化学物种被确凿地证明符合观察到的金星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。这将首先在散装的液体或气溶胶分布中完成，然后使用光学镊子在单个液滴中完成。该项目还将考虑液滴中候选吸收体的物理和更一般的光学性质，包括实际折射率和保持球形形状的能力。金星上观察到了光辉图案--一系列同心彩色光环，当光线在内部反射时，球形水滴会产生这些光环(Laven，2005)。观察到的光辉表明液滴中存在吸收颗粒。粒子必须完全在液滴内，因为将粒子附着到液滴表面会导致光泽扭曲，这是看不到的。一些候选者不可能插入到液滴中，因此，无论它们与光学性质和检测到的吸收是否一致，都不可能是吸收体(Petrova，2018)。LMD(Le Labatoire de Météorologie Dynamique)金星大气模型全面模拟了金星的云层。可以将实验室实验中有希望的候选者的物理、化学和光学性质包括在模型中，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宜性。除了帮助缩小搜索范围或加强识别吸收体的证据外，在模型中包括确认的吸收体还将提高其模拟现实行为以解决其他问题的能力。如果没有一个单一的候选对象似乎足以提供所有检测到的吸收，计算机建模将特别有用。然后，将使用建模来组合不同数量和配对的候选吸收体，以查看是否有任何有希望的吸收体。如果预测到有希望的候选混合物，就可以开始对混合物进行实验测试，这个过程可以迭代进行，以确定吸波比。

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.