Aerosols are common in the atmospheres of exoplanets across a wide swath of temperatures, masses and ages^1,2,3. These aerosols strongly impact observations of transmitted, reflected and emitted light from exoplanets, obfuscating our understanding of exoplanet thermal structure and composition^4,5,6. Knowing the dominant aerosol composition would facilitate interpretations of exoplanet observations and theoretical understanding of their atmospheres. A variety of compositions have been proposed, including metal oxides and sulfides, iron, chromium, sulfur and hydrocarbons^7,8,9,10,11. However, the relative contributions of these species to exoplanet aerosol opacity is unknown. Here we show that the aerosol composition of giant exoplanets observed in transmission is dominated by silicates and hydrocarbons. By constraining an aerosol microphysics model with trends in giant exoplanet transmission spectra, we find that silicates dominate aerosol opacity above planetary equilibrium temperatures of 950 K due to low nucleation energy barriers and high elemental abundances, while hydrocarbon aerosols dominate below 950 K due to an increase in methane abundance. Our results are robust to variations in planet gravity and atmospheric metallicity within the range of most giant transiting exoplanets. We predict that spectral signatures of condensed silicates in the mid-infrared are most prominent for hot (>1,600 K), low-gravity (<10 m s⁻²) objects.

气溶胶普遍存在于系外行星大气中，温度，质量和年龄分别为^1,2,3。这些气溶胶强烈影响着系外行星的透射，反射和发射光的观测，使我们对系外行星的热结构和成分^4,5,6的理解变得模糊。知道主要的气溶胶成分将有助于解释系外行星的观测结果和对其大气的理论理解。已经提出了多种组成，包括金属氧化物和硫化物，铁，铬，硫和碳氢化合物^7,8,9,10,11。但是，这些物种对系外行星气溶胶不透明度的相对贡献尚不清楚。在这里，我们表明，在传播过程中观察到的巨大系外行星的气溶胶成分以硅酸盐和碳氢化合物为主。通过用巨大的系外行星透射光谱趋势约束气溶胶微观物理模型，我们发现，由于低成核能垒和高元素丰度，在高于950 K的行星平衡温度下，硅酸盐主导着气溶胶的不透明性，而由于增加，碳氢化合物的气溶胶在950 K以下占主导地位。甲烷含量高 我们的结果对于在大多数巨型过境系外行星范围内的行星重力和大气金属度变化具有鲁棒性。我们预测，在高温（> 1,600 K），低重力（<< 1,600 K）下，中红外处的冷凝硅酸盐的光谱特征最为突出。⁻²）对象。