AI 中文总结
本研究通过JWST NIRISS/SOSS光谱探测到WASP-69 b晨昏线的不对称气溶胶分布，揭示暖巨行星气溶胶分布过渡阶段的特征，为理解系外行星气溶胶循环提供观测依据。
AI 中文摘要
气溶胶如何在系外行星的温度范围内形成、传输并在凝结与蒸发之间循环，目前仍知之甚少。近期模型与观测表明，温度约800至1000开尔文的暖巨行星可能处于均匀与经度异质气溶胶分布之间的过渡阶段。我们利用JWST NIRISS/SOSS获取的WASP-69 b的0.86至2.82微米透射光谱，对一颗平衡温度≤1000开尔文的巨行星的气溶胶不对称性进行了可靠探测：昏侧 limb 呈现显著的1.4微米H₂O吸收（ΔBIC_H₂O=+22.7），而晨侧 limb 未探测到H₂O（ΔBIC_H₂O=-8.7）。大气反演显示两侧 limb 均存在显著的气溶胶不透明度，晨侧 limb 因高海拔、光学厚的云层掩盖了分子特征，而较低的云不透明度使昏侧 limb 的H₂O得以显现。昏侧晨昏线温度比晨侧高304⁺⁶²₋₉¹开尔文，与晨侧凝结物向昏侧传输时部分蒸发的机制一致，该机制通过三维全球环流模型得到独立验证。恒星污染或光化学霾主导的气溶胶难以解释这种不对称性。通过 limb 分辨分析，我们推断其大气金属丰度为恒星至超恒星水平，平衡反演得到[M/H]=0.11⁺⁰.⁴⁰₋₀.₄₆，自由反演得到[O/H]=1.38⁺⁰.⁴⁴₋₀.⁷⁹；还探测到延伸至3.08⁺⁰.⁵⁰₋₀.₄₅倍行星半径的逃逸亚稳态氦尾。WASP-69 b是新兴的不对称气溶胶分布行星群中温度较低的边缘成员，表明在该过渡阶段两侧 limb 可能持续存在显著的气溶胶不透明度。
英文摘要
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 $0.86$--$2.82~μ$m JWST NIRISS/SOSS transmission spectrum of WASP-69 b. The evening limb shows prominent 1.4 $μ$m H$_2$O absorption ($Δ\mathrm{BIC}_{\rm H_2O}=+22.7$), whereas H$_2$O is not detected on the morning limb ($Δ\mathrm{BIC}_{\rm H_2O}=-8.7$). 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 extending to $3.08^{+0.50}_{-0.45}\,R_p$. WASP-69 b anchors the cooler edge of the emerging population of planets with asymmetric aerosol distributions and suggests that substantial aerosol opacity may persist on both limbs across this transition.
Comments24 pages, 11 figures, 6 tables, submitted to ApJL
