The atmospheric properties of hot exoplanets are expected to be different between the morning and the evening limbs due to their global atmospheric circulation. Ground-based observations at high spectral resolution have detected this limb asymmetry in several ultra-hot (>2,000 K) exoplanets, but the prevalence of the phenomenon in the broader exoplanetary population remains unexplored. Here we use JWST/NIRCam transmission spectra between 2.5 and 4.0 μm to find evidence of limb asymmetry on exoplanet WASP-107 b. With its equilibrium temperature of 770 K and low density of 0.126 g cm⁻³, WASP-107 b probes a very different regime compared to ultra-hot giant planets and was not expected to exhibit substantial spatial heterogeneity according to atmospheric models. We infer instead a morning-to-evening temperature difference of the order of 100 K with a hotter evening limb. Further observations of other cooler exoplanets are needed to determine whether WASP-107 b is an outlier or whether the models have underestimated the presence of limb asymmetry in exoplanets.

由于其全球大气环流，热系外行星的大气特性预计在早晨和傍晚之间会有所不同。高光谱分辨率的地面观测已在几颗超热 (>2,000 K) 系外行星中检测到这种肢体不对称性，但这种现象在更广泛的系外行星群体中的普遍程度仍未得到探索。在这里，我们使用 2.5 至 4.0 μm 之间的 JWST/NIRCam 透射光谱来寻找系外行星 WASP-107 b 上肢体不对称的证据。凭借 770 K 的平衡温度和 0.126 g cm ^-3的低密度，WASP-107 b 与超热巨行星相比探测到了非常不同的状态，并且根据大气模型预计不会表现出显着的空间异质性。相反，我们推断早晚温差约为 100 K，傍晚温度更高。需要对其他较冷的系外行星进行进一步观察，以确定 WASP-107 b 是否是异常值，或者模型是否低估了系外行星中肢体不对称的存在。