近日，美国芝加哥大学的Jacob L.Bean与亚利桑那大学的Megan Mansfield等人合作，研究了土星质量行星的高大气金属富集。相关成果已于2023年3月27日在国际权威学术期刊《自然》上发表。
该研究发现，土星质量的系外行星HD 149026b的大气金属度为太阳金属度的59-276倍（置信度为1σ），这比土星大气金属度高出约7.5倍太阳金属度（置信度> 4σ）。这个结果基于使用JWST测量的行星热发射光谱中CO2和H2O吸收特征的建模。HD 149026b是已知最富含金属的巨型行星，估计重元素丰度按质量计算为66±2%。研究发现，HD 149026b和太阳系巨型行星的大气金属度与体积金属度更相关，而非行星质量。
据介绍，大气金属富集（即比氦重的元素，也称“金属度”）是巨型行星形成的关键诊断因素。太阳系的巨型行星表现出质量与它们的体积金属度和大气金属度之间的反比关系。太阳系外的巨型行星也显示出质量和体积金属度之间的反比关系，但是这种关系存在显著的发散，并且尚不清楚大气金属度与行星质量或体积金属度之间的关系。
附：英文原文
Title: High atmospheric metal enrichment for a Saturn-mass planet
Author: Bean, Jacob L., Xue, Qiao, August, Prune C., Lunine, Jonathan, Zhang, Michael, Thorngren, Daniel, Tsai, Shang-Min, Stassun, Keivan G., Schlawin, Everett, Ahrer, Eva-Maria, Ih, Jegug, Mansfield, Megan
Issue&Volume: 2023-03-27
Abstract: Atmospheric metal enrichment (i.e., elements heavier than helium, also called “metallicity”) is a key diagnostic of the formation of giant planets1-3. The giant planets of the solar system exhibit 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 metallicity4. 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 149026b5-9 has an atmospheric metallicity 59 - 276 times solar (at 1σ), which is greater than Saturn’s atmospheric metallicity of ~7.5 times solar10 at >4σ confidence. This result is based on modeling CO2 and H2O absorption features in the thermal emission spectrum of the planet measured by JWST. HD 149026b is the most metal-rich giant planet known, with an estimated bulk heavy element abundance of 66±2% by mass11,12. 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.
DOI: 10.1038/s41586-023-05984-y
