Products and Models for "Early Release Science of the Exoplanet WASP-39b with JWST NIRISS"

Associated Publication: https://www.nature.com/articles/s41586-022-05674-1 Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans 0.6−2.8μm in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as signatures of clouds. The precision and broad wavelength coverage of NIRISS-SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favoring a heavy element enhancement ("metallicity") of ∼10−30× the solar value, a sub-solar carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator.关联论文：https://www.nature.com/articles/s41586-022-05674-1 透射光谱（Transmission spectroscopy）可为凌日系外行星的大气特性，进而为其形成历史、物理过程与化学过程提供研究见解。然而，若要从透射光谱中精准推断系外行星的大气特性，需同时测量多种化学物种的多条光谱吸收特征的强度与轮廓。受限于既往观测台站的精度与波长覆盖范围，此前实现这一点颇具挑战。 本研究展示了利用詹姆斯·韦布空间望远镜（James Webb Space Telescope, JWST）上的近红外成像仪与无缝隙光谱仪（Near-Infrared Imager and Slitless Spectrograph, NIRISS）的SOSS模式，获取的土星质量凌日系外行星WASP-39b的透射光谱。该光谱的波长覆盖范围为0.6−2.8μm，揭示了多条水汽吸收带、钾共振双线以及云系信号。 NIRISS-SOSS的高精度与宽波长覆盖范围，使得我们得以破解WASP-39b云系特性与大气成分之间的模型简并问题，研究结果支持重元素丰度（金属丰度"metallicity"）约为太阳值的10−30倍、碳氧比（C/O）低于太阳值、钾氧比（K/O）介于太阳值至超太阳值之间。观测结果最符合的模型为：覆盖行星晨昏线（terminator）不均匀且具有波长依赖性的非灰体云系。