Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
School of Physics and Astronomy, Shanghai Jiaotong University, Shanghai, China.
Nature. 2023 Jun;618(7963):43-46. doi: 10.1038/s41586-023-05984-y. Epub 2023 Mar 27.
Atmospheric metal enrichment (that is, elements heavier than helium, also called 'metallicity') is a key diagnostic of the formation of giant planets. The giant planets of the Solar System show an inverse relationship between mass and both their bulk metallicities and atmospheric metallicities. Extrasolar giant planets also display an inverse relationship between mass and bulk metallicity. However, there is significant scatter in the relationship and it is not known how atmospheric metallicity correlates with either planet mass or bulk metallicity. Here we show that the Saturn-mass exoplanet HD 149026b (refs. ) has an atmospheric metallicity 59-276 times solar (at 1σ), which is greater than Saturn's atmospheric metallicity of roughly 7.5 times solar at more than 4σ confidence. This result is based on modelling CO and HO absorption features in the thermal emission spectrum of the planet measured by the James Webb Space Telescope. HD 149026b is the most metal-rich giant planet known, with an estimated bulk heavy element abundance of 66 ± 2% by mass. We find that the atmospheric metallicities of both HD 149026b and the Solar System giant planets are more correlated with bulk metallicity than planet mass.
大气金属丰度（即氦以上的元素，也称为“金属丰度”）是形成巨行星的关键诊断指标。太阳系中的巨行星的质量与其体金属丰度和大气金属丰度呈反比关系。系外巨行星的质量与其体金属丰度也呈反比关系。然而，这种关系存在显著的离散性，目前尚不清楚大气金属丰度与行星质量或体金属丰度如何相关。在这里，我们表明，土星质量的系外行星 HD 149026b（参考文献）的大气金属丰度是太阳的 59-276 倍（在 1σ 范围内），这比土星大气金属丰度高约 7.5 倍，置信度超过 4σ。这一结果是基于对该行星热发射光谱中 CO 和 HO 吸收特征的建模得出的，这些特征是由詹姆斯·韦伯太空望远镜测量的。HD 149026b 是已知的金属丰度最高的巨行星之一，其体重元素丰度估计为 66±2%。我们发现，HD 149026b 和太阳系巨行星的大气金属丰度与体金属丰度的相关性都高于与行星质量的相关性。
