Products and Models for "Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b"

Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5-12 μm with JWST's Mid-Infrared Instrument (MIRI). The spectra reveal a large day-night temperature contrast (with average brightness temperatures of 1524±35 and 863±23 Kelvin, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase curve shape and emission spectra strongly suggest the presence of nightside clouds which become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2σ upper limit of 1-6 parts per million, depending on model assumptions).

热木星（Hot Jupiters）是目前研究最为深入的系外行星之一，但学界对其化学成分与云系属性随经度的变化规律仍知之甚少。理论模型预测，云系或可在行星夜侧凝结，且纬向风可打破分子丰度的平衡状态。本研究报告了利用詹姆斯·韦伯太空望远镜（James Webb Space Telescope, JWST）的中红外仪器（Mid-Infrared Instrument, MIRI）在5至12微米波段测得的热木星WASP-43b的相分辨发射光谱。该光谱显示出显著的昼夜温差：昼侧平均亮温为1524±35开尔文，夜侧为863±23开尔文，且在所有轨道相位中均检测到水分子吸收信号。通过与三维大气模型比对可知，相曲线形态与发射光谱均强烈表明夜侧存在云系：当压强高于约100毫巴时，该云系对热辐射呈光学厚状态。昼侧中红外光球层以上的大气则无云系存在，与观测结果相符。与平衡化学理论的预期相悖，但与非平衡动力学模型相符的是，研究未在夜侧检测到甲烷（根据模型假设不同，其2σ置信上限为1至6百万分比浓度）。