热化学模型下天王星与海王星的大气垂直结构：模型假设的影响
The atmospheric vertical structure of Uranus and Neptune from thermochemical models: the impact of model assumptions
AI总结：
本研究利用FastChem代码探究金属丰度、元素比值等模型假设对天王星与海王星大气垂直结构的影响，发现模型参数敏感性高，需后续观测与专项任务明确其大气特征。
AI中文摘要：
天王星与海王星的大气成分及温度-压力剖面尚未得到准确测定。由于观测数据有限，人们常依赖化学平衡计算来推断大气丰度与云的形成。然而，推断出的大气结构高度依赖于若干基本假设，如元素丰度与比值、所假设物质的凝结特性，或绝热结构的参考温度。本研究探究了不同金属丰度（1至80倍太阳丰度）、元素比值（C/O为0.1至2，S/N为0.19至1.6）以及1巴温度（66至86开尔文）对冰巨行星大气垂直结构的影响。具体而言，我们使用化学平衡代码FastChem推导CH₄、NH₃、H₂S、H₂O和NH₄SH的混合比与云结构。研究发现，模型对所假设参数极为敏感，会产生截然不同的可能大气结构；在本研究考虑的案例中，混合比与云顶高度的变化可超过一个数量级，且热剖面因成分与1巴温度的差异可相差数十开尔文。我们建议未来需开展地基观测及针对天王星和/或海王星的专项任务，以更好地表征冰巨行星的大气结构与成分。
英文摘要：
The composition and temperature-pressure profile of the atmospheres of Uranus and Neptune are not well-determined. As observational data are limited, we often rely on chemical equilibrium computations to infer atmospheric abundances and cloud formation. The inferred atmospheric structures, however, strongly depend on several fundamental assumptions such as the elemental abundances and ratios, the condensation properties of the assumed species, or a reference temperature for the adiabatic structure. In this study we investigate the effects of different metallicities (1 to 80 solar), element ratios (C/O and S/N, from 0.1 to 2 and 0.19 to 1.6) and 1 bar temperatures (66 to 86 K) on the vertical structure of ice giant atmospheres. In particular, we use the chemical equilibrium code \texttt{FastChem} to derive mixing ratios and cloud structures for CH$_4$, NH$_3$, H$_2$S, H$_2$O and NH$_4$SH. We find that the models are very sensitive to the assumed parameters, yielding drastically different possible atmospheric structures. For the cases considered here, we find that mixing ratios and cloud deck altitudes can vary by more than an order of magnitude. Additionally, thermal profiles can differ by several tens of kelvins due to composition and 1-bar temperature. We advise that future ground-based observations and a dedicated mission to Uranus and/or Neptune are required to better characterize the atmospheric structure and composition of ice giants.
