气态巨行星并非完全混合
Giant exoplanets are not fully mixed
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中文总结 AI 辅助
该研究利用JWST数据发现多数暖巨行星内部并非完全混合，大气金属丰度无法代表整体成分，混合不充分是普遍现象，且太阳系巨行星无异常，或表明部分混合是巨行星形成的普遍结果。
中文摘要 AI 辅助
气态巨行星的内部结构与整体成分无法直接观测，必须通过模型推断。在常见假设中，行星包层混合充分且处于绝热状态，测得的大气金属丰度被用作整个包层金属丰度的替代指标，进而代表行星的重元素总量。詹姆斯·韦布空间望远镜（JWST）现已为越来越多的暖巨行星提供了精确的大气金属丰度，使这一假设首次得以检验。我们量化了暖巨行星包层与整体金属丰度的差异，以评估成分分层的证据。我们收集了11颗拥有JWST反演得到的大气金属丰度的暖巨行星，为每颗行星计算定制化的内部与热演化模型网格，并开展马尔可夫链蒙特卡洛（MCMC）反演，以推断与测得的质量、半径、系统年龄及大气金属丰度相符的整体金属丰度。样本中所有行星的包层金属丰度均小于整体金属丰度，混合比例约为0.02至0.90；11颗行星中有8颗的混合比例低于0.50，10颗行星的结果与完全混合的内部结构在1倍标准差范围内不一致。我们初步发现行星质量与包层金属丰度之间存在显著的负相关，但包层与整体金属丰度、包层与宿主恒星金属丰度之间无相关性。因此，大气金属丰度并非暖巨行星整体成分的可靠替代指标，在JWST可观测的行星中，混合不充分（可能存在成分梯度）似乎是普遍现象；假设包层均匀的整体成分估计会大幅低估总重元素质量。而太阳系巨行星在该样本中并无异常，这表明稀释或部分混合的内部结构可能是巨行星形成的普遍结果。
英文摘要
The interior structure and bulk composition of giant planets are not directly observable and must be inferred from models. Under the common assumption of a well-mixed, adiabatic envelope, the measured atmospheric metallicity is taken as a proxy for the metallicity of the entire envelope, and hence for the planet's heavy-element budget. JWST now provides precise atmospheric metallicities for a growing number of warm giants, allowing this assumption to be tested for the first time. We quantify the difference between envelope and bulk metallicities of warm giants to assess the evidence for compositional stratification. We assembled eleven warm giants with atmospheric metallicities from published JWST retrievals, computed tailored interior and thermal evolution model grids for each, and performed MCMC retrievals to infer the bulk metallicity consistent with the measured mass, radius, system age, and atmospheric metallicity. Envelope metallicities are smaller than bulk metallicities throughout the sample, with mixing ratios from about 0.02 to 0.90. Eight of the eleven planets have mixing ratios below 0.50, and ten are inconsistent with a fully mixed interior to within one sigma. We tentatively identify a significant anti-correlation between planetary mass and envelope metallicity, but no correlation between envelope and bulk metallicity, nor between envelope and host-star metallicity. Atmospheric metallicity is therefore not a reliable proxy for the bulk composition of warm giants, and incomplete mixing (possibly composition gradients) appears common among the planets accessible to JWST. Bulk composition estimates assuming a homogeneous envelope substantially underestimate the total heavy-element mass. That the solar-system giants are unremarkable within this sample suggests dilute or partially mixed interiors may be a generic outcome of giant planet formation.
