论文标题
在JWST Niriss/Soss的HAT-P-18B的朦胧和甲烷消耗的氛围中检测到的水和逃避的氦气尾巴
Water and an escaping helium tail detected in the hazy and methane-depleted atmosphere of HAT-P-18b from JWST NIRISS/SOSS
论文作者
论文摘要
JWST在这里。早期发布观察计划（ERO）为我们提供了科学数据和光谱功能的首次查看。 ERO的目标之一是Hat-P-18B，这是一个充气的土星质量行星，平衡温度为$ \ sim $ 850K。我们将HAT-P-18B的NIRIS/SOSS传输频谱从0.6到2.8 $μm$ $，并首次在红外线中揭示了该行星，这是第一次超过1.6 $μm$。从光谱中，我们可以在原本朦胧的气氛中看到透明的水和逃避氦气尾巴的特征。我们使用ATMO的自由化学检索显示了支持甲烷的存在的中等贝叶斯证据（3.79），但频谱没有显示出任何可明显可识别的甲烷吸收特征。检索到的甲烷丰度为$ \ sim $ 2比太阳能成分低的数量级。甲烷耗尽的大气强烈拒绝具有太阳金属性和C/O比的简单平衡化学前进模型，并且不散发高金属性（100倍）和低C/O比（0.3）。这需要其他物理过程，例如垂直混合和光化学，可以从大气中去除甲烷。
JWST is here. The early release observation program (ERO) provides us with the first look at the scientific data and the spectral capabilities. One of the targets from ERO is HAT-P-18b, an inflated Saturn-mass planet with an equilibrium temperature of $\sim$850K. We present the NIRISS/SOSS transmission spectrum of HAT-P-18b from 0.6 to 2.8$μm$ and reveal the planet in the infrared beyond 1.6$μm$ for the first time. From the spectrum, we see clear water and escaping helium tail features in an otherwise very hazy atmosphere. Our free chemistry retrievals with ATMO show moderate Bayesian evidence (3.79) supporting the presence of methane, but the spectrum does not display any clearly identifiable methane absorption features. The retrieved methane abundance is $\sim$2 orders of magnitude lower than that of solar composition. The methane-depleted atmosphere strongly rejects simple equilibrium chemistry forward models with solar metallicity and C/O ratio and disfavors high metallicity (100 times) and low C/O ratio (0.3). This calls for additional physical processes such as vertical mixing and photochemistry which can remove methane from the atmosphere.
