韦布空间望远镜（JWST）NIRISS/SOSS 揭示温热土星（Saturn）WASP-69 b 晨昏线上的非对称气溶胶分布

本文利用韦布空间望远镜（JWST）的观测数据，分析了系外行星（exoplanet）WASP-69 b 的透射光谱。研究发现该行星晨昏线上的气溶胶分布存在显著的不对称性，晨昏两侧云层不透明度的差异导致了水汽特征的观测结果不同。这一现象与总环流（general circulation）模型中晨侧凝结物向昏侧输运并蒸发的机制相符。

arXiv:2608.19756v1 Announce Type: new Abstract: How aerosols form, are transported, and cycle between condensation and evaporation across exoplanet temperature regimes remains poorly understood. Recent models and observations suggest that warm giant planets near $800$--$1000$ K may span a transition between homogeneous and longitudinally heterogeneous aerosol distributions. We present a robust detection of aerosol asymmetry in a giant planet with $T_{\rm eq}\lesssim1000$ K, using the $0.86$--$2.82~\mu$m JWST NIRISS/SOSS transmission spectrum of WASP-69 b. The evening limb shows prominent 1.4 $\mu$m H$_2$O absorption ($\Delta\mathrm{BIC}_{\rm H_2O}=+22.7$), whereas H$_2$O is not detected on the morning limb ($\Delta\mathrm{BIC}_{\rm H_2O}=-8.7$). Atmospheric retrievals reveal significant aerosol opacity on both limbs, with high-altitude, optically thick clouds muting molecular features on the morning limb and lower cloud opacity allowing H$_2$O to emerge on the evening limb. The evening terminator is hotter by $304^{+62}_{-91}$ K, consistent with morning-limb condensates partially evaporating during transport toward the evening limb. This mechanism is independently verified with 3D general circulation models. Stellar contamination or aerosols dominated by photochemical haze do not readily explain the asymmetry. From a limb-resolved analysis, we infer a stellar-to-superstellar atmospheric metallicity, with $\rm[M/H]=0.11^{+0.40}_{-0.46}$ from the equilibrium retrieval and [O/H]$=1.38^{+0.44}_{-0.79}$ from the free retrieval. We also detect an escaping metastable-helium tail