发表机构
Aix-Marseille Université; Southwest Research Institute; Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux; Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité; University of Science and Technology of China; Dublin Institute for Advanced Studies; Space Science Institute（艾克斯-马赛大学; 西南研究院; 波尔多大学天体物理实验室; 巴黎天文台、巴黎文理研究大学、法国国家科学研究中心、索邦大学、巴黎西岱大学; 中国科学技术大学; 都柏林高等研究所; 空间科学研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过扩展模型分析天王星与海王星的非平衡化学，发现二者C/O比、氧丰度存在差异，支持其演化路径不同，还为未来天王星探测任务提供了框架。
AI 中文摘要
天王星与海王星的形成过程仍缺乏明确约束，很大程度上源于其内部元素丰度的不确定性。一氧化碳（CO）是对流层上层的一种非平衡物种，可间接约束内部氧丰度。我们通过考虑大气结构的经向变化与化学动力学的不确定性，研究冰巨行星的内部氧氢比（O/H）、碳氧比（C/O）及其形成历史。我们将一维热化学与扩散模型扩展为伪二维模型，纳入关键模型参数的纬度变化。通过将模拟的对流层上层CO摩尔分数与观测值匹配，反演得到O/H比，结合内部碳丰度推导C/O比。对于天王星，仅改变对流层甲烷时，O/H约为原太阳的[47-57]倍；若允许垂直涡扩散系数（Kzz）变化，范围扩大至O/H约为原太阳的[62-177]倍。对应地，海王星的O/H范围分别为原太阳的[182-215]倍和[222-342]倍，支持天王星的氧富集程度低于海王星。化学网络不确定性的影响较小，仅占反演氧范围的约10%，与海王星实测CO丰度的不确定性相当，但在天王星上影响更大。我们计算了C/O的纬度范围，发现天王星约为[0.06-0.52]，海王星约为[0.02-0.12]。与原行星盘模型对比表明，两颗行星的形成或演化路径不同。本研究强调了垂直混合在约束内部氧丰度中的主导作用，以及考虑经向变异性和化学不确定性的重要性，还为未来天王星轨道飞行器与探测任务的进入纬度选择提供了框架。
英文摘要
The formation of Uranus and Neptune remains poorly constrained largely due to uncertain deep elemental abundances. Carbon monoxide (CO), a disequilibrium species in the upper troposphere, provides an indirect constraint on the deep oxygen abundance. We investigate the deep O/H and C/O ratios of the ice giants and their formation history by accounting for meridional variations in atmospheric structure and uncertainties in chemical kinetics. We extended a 1D thermochemical and diffusion model into a pseudo-2D model by including latitudinal variations in key model parameters. The O/H ratio was inferred by matching the modeled upper-tropospheric CO mole fractions to observations, and combined with the deep carbon abundance to derive the C/O ratio. For Uranus, varying tropospheric methane alone yielded O/H $\sim [47-57] \times$ protosolar, whereas allowing $K_{zz}$ to vary expanded the range to O/H $\sim [62-177] \times$ protosolar. For Neptune, the corresponding ranges are O/H $\sim [182-215] \times$ protosolar and O/H $\sim [222-342] \times$ protosolar, respectively, supporting lower oxygen enrichment in Uranus than Neptune. Chemical-network uncertainties have a more modest effect, amounting to at most $\sim 10\%$ of the retrieved oxygen ranges, comparable to the uncertainty associated with the measured CO abundance on Neptune, but larger on Uranus. We computed C/O latitudinal ranges and found C/O $\sim [0.06-0.52]$ on Uranus and $\sim [0.02-0.12]$ on Neptune. Comparison with a protoplanetary disk model suggests different formation or evolutionary pathways for the two planets. Our results highlight the dominant role of vertical mixing in constraining deep oxygen abundance and the importance of accounting for meridional variability and chemical uncertainties. This work also provides a framework for selecting the entry latitude of a future Uranus Orbiter and Probe mission.
Comments35 pages, 10 figures To be published in A&A
DOI：10.1051/0004-6361/202660770
