Observations of exoplanet atmospheres have shown that aerosols, like in the solar system, are common across a variety of temperatures and planet types. The formation and distribution of these aerosols are inextricably intertwined with the composition and thermal structure of the atmosphere. At the same time, these aerosols also interfere with our probes of atmospheric composition and thermal structure, and thus a better understanding of aerosols lead to a better understanding of exoplanet atmospheres as a whole. Here we review the current state of knowledge of exoplanet aerosols as determined from observations, modeling, and laboratory experiments. Measurements of the transmission spectra, dayside emission, and phase curves of transiting exoplanets, as well as the emission spectrum and light curves of directly imaged exoplanets and brown dwarfs have shown that aerosols are distributed inhomogeneously in exoplanet atmospheres, with aerosol distributions varying significantly with planet equilibrium temperature and gravity. Parameterized and microphysical models predict that these aerosols are likely composed of oxidized minerals like silicates for the hottest exoplanets, while at lower temperatures the dominant aerosols may be composed of alkali salts and sulfides. Particles originating from photochemical processes are also likely at low temperatures, though their formation process is highly complex, as revealed by laboratory work. In the years to come, new ground‐ and space‐based observatories will have the capability to assess the composition of exoplanet aerosols, while new modeling and laboratory efforts will improve upon our picture of aerosol formation and dynamics.

中文翻译：

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系外行星大气中的气溶胶

系外行星大气层的观测表明，像太阳系一样，气溶胶在各种温度和行星类型中都很常见。这些气溶胶的形成和分布与大气的成分和热结构密不可分。同时，这些气溶胶还会干扰我们对大气成分和热结构的探测，因此，对气溶胶的更好理解会导致对整个系外行星大气的更好理解。在这里，我们回顾从观测，建模和实验室实验确定的系外行星气溶胶的当前知识状态。测量透射系外行星的透射光谱，日间发射和相位曲线，直接成像的系外行星和褐矮星的发射光谱和光曲线表明，气溶胶在系外行星大气中分布不均匀，气溶胶的分布随行星平衡温度和重力的变化而显着变化。参数化模型和微物理模型预测，这些气溶胶可能由氧化矿物组成，例如最热的系外行星的硅酸盐，而在较低温度下，主要气溶胶可能由碱金属盐和硫化物组成。正如实验室工作所揭示的那样，源自光化学过程的颗粒也可能在低温下运行，尽管它们的形成过程非常复杂。在未来的几年中，新的地面和空间天文台将有能力评估系外行星气溶胶的组成，