美国约翰霍普金斯大学Fu Guangwei小组近日研究了木星质量大小的系外行星的硫化氢和富含金属的大气层。相关论文于2024年7月8日发表在《自然》杂志上。

据研究人员介绍，作为距离地球最近的凌日热木星，HD189733b一直是大气表征的基准行星。从成分、化学、气溶胶到大气动力学、逃逸和建模技术，它也是人们对系外行星大气的许多理论理解的锚点。先前对HD189733b的研究已经在大气中检测到含碳和含氧分子H₂O和CO，CO₂和CH₄的存在已经被证实，但后来又引起一定的争议。基于这些测量推断出的金属丰度是追踪行星形成位置的关键参数，但金属丰度从衰减到增强受波长覆盖范围和观测精度的限制。

研究人员报道在HD189733b的透射光谱(2.4-5micron)中检测到H₂O(13.4sigama)，CO₂(11.2sigama)，CO(5sigama)和H₂S(4.5sigama)。平衡温度约为1200K，H₂O、CO和H₂S是氧、碳和硫的主要储存库。根据测量的这三种主要挥发性元素的丰度，研究人员推断大气的金属丰度是恒星的3-5倍。5 sigama处甲烷丰度的上限为0.1ppm，碳氧比较低(<0.2)，表明是通过富含水的冰态星子吸积形成的。低氧硫比和低碳硫比也支持星子吸积的形成途径。

附：英文原文

Title: Hydrogen sulfide and metal-enriched atmosphere for a Jupiter-mass exoplanet

Author: Fu, Guangwei, Welbanks, Luis, Deming, Drake, Inglis, Julie, Zhang, Michael, Lothringer, Joshua, Ih, Jegug, Moses, Julianne I., Schlawin, Everett, Knutson, Heather A., Henry, Gregory, Greene, Thomas, Sing, David K., Savel, Arjun B., Kempton, Eliza M.-R., Louie, Dana R., Line, Michael, Nixon, Matt

Issue&Volume: 2024-07-08

Abstract: As the closest transiting hot Jupiter to Earth, HD 189733b has been the benchmark planet for atmospheric characterization. It has also been the anchor point for much of our theoretical understanding of exoplanet atmospheres from composition, chemistry, aerosols to atmospheric dynamics escape and modeling techniques. Prior studies of HD 189733b have detected carbon and oxygen-bearing molecules H₂O and CO in the atmosphere. The presence of CO₂ and CH₄ has been claimed but later disputed. The inferred metallicity based on these measurements, a key parameter in tracing planet formation locations, varies from depletion to enhancement, hindered by limited wavelength coverage and precision of the observations. Here we report detections of H₂O (13.4 sigma), CO₂ (11.2 sigma), CO (5 sigma), and H₂S (4.5 sigma) in the transmission spectrum (2.4-5 micron) of HD 189733b. With an equilibrium temperature of~1200K, H₂O, CO, and H₂S are the main reservoirs for oxygen, carbon, and sulfur. Based on the measured abundances of these three major volatile elements, we infer an atmospheric metallicity of 3-5 times stellar. The upper limit on the methane abundance at 5 sigma is 0.1 ppm which indicates a low carbon-to-oxygen ratio (<0.2), suggesting formation through the accretion of water-rich icy planetesimals. The low oxygen-to-sulfur and carbon-to-sulfur ratios also support the planetesimal accretion formation pathway.

DOI: 10.1038/s41586-024-07760-y

Source: https://www.nature.com/articles/s41586-024-07760-y