标题： 多云的早晨和晴朗的夜晚在热木星系外行星大气中 显示英文标题

标题： Overcast mornings and clear evenings in hot Jupiter exoplanet atmospheres

摘要： 气溶胶是系外行星大气这一年轻领域中的一个古老话题。 理解它们是什么，如何形成，以及它们去向何处，长期以来为理论家提供了一个丰富的研究领域。 然而，对于观测者来说，气溶胶多年来一直是个令人头痛的问题，因为它们的持续存在掩盖了大气特征。 对于热木星而言，昼夜之间巨大的温度差异驱动了不均匀的热结构和气溶胶分布，导致通过凌日光谱探测到的不同边缘特性。 我们展示了九颗气体巨行星的JWST NIRISS/SOSS光谱，其平衡温度约为800-1700 K。通过测量两个边缘的1.4$\mu$m水带特征大小，我们发现三颗行星（WASP-39 b、WASP-94 Ab和WASP-17 b）显示出显著的（$>$5$\sigma$）边缘-边缘大气消光差异，其中早晨边缘较弱，而傍晚边缘清晰。 早晨边缘上强烈的水特征表明高海拔（0.1至0.01 mbar）气溶胶。 要同时拥有清晰的傍晚边缘，需要时间尺度（$\sim$天）与平流相当的过程来移除这些悬浮颗粒，我们发现下沉流动和白天云层蒸发都可能是可行的机制。 我们假设了一个经验边界——称为“不对称地平线”——在温度-重力空间中，标志着不均匀气溶胶覆盖开始出现的过渡区域。 热木星中异质气溶胶覆盖很常见。 如果未被识别，边缘平均会抑制光谱特征，模仿高平均分子量的大气，使推断的金属量增加高达2个数量级，并低估边缘温度多达一半。 最后，我们引入了边缘光谱度量（LSM），根据行星参数预测边缘光谱特征大小。 显示英文摘要

摘要： Aerosols is an old topic in the young field of exoplanet atmospheres. Understanding what they are, how they form, and where they go has long provided a fertile playground for theorists. For observers, however, aerosols have been a multi-decade migraine, as their chronic presence hides atmospheric features. For hot Jupiters, the large day-night temperature contrast drives inhomogeneous thermal structures and aerosol distribution, leading to different limb properties probed by transit spectra. We present JWST NIRISS/SOSS spectra of morning and evening limbs for nine gas giants with equilibrium temperatures of ~800-1700 K. By measuring feature size of the 1.4 $\mu$m water band for both limbs, we found three planets (WASP-39 b, WASP-94 Ab, and WASP-17 b) show prominent ($>$5$\sigma$) limb-limb atmospheric opacity difference with muted morning and clear evening limbs. The heavily muted water features on morning limbs indicate high-altitude (0.1 to 0.01 mbar) aerosols. To simultaneously have clear evening limbs requires processes with timescales ($\sim$day) comparable to advection to remove these lofted grains, and we found that both downwelling flow and dayside cloud evaporation could be plausible mechanisms. We hypothesize an empirical boundary--termed the "asymmetry horizon"--in temperature-gravity space that marks the transition where inhomogeneous aerosol coverage begins to emerge. Heterogeneous aerosol coverage is common among hot Jupiters. If unrecognized, limb averaging suppresses spectral features, mimicking high-mean-molecular-weight atmospheres, inflating inferred metallicity by up to 2 dex, and underestimating limb temperatures by as much as half. Finally, we introduce the Limb Spectroscopy Metric (LSM) to predict limb spectral feature size based on planet parameters.