论文标题
天王星和海王星的热力学控制的内部模型
Thermodynamically Governed Interior Models of Uranus and Neptune
论文作者
论文摘要
天王星和海王星的内部模型通常假设离散层，但是只有在主要成分不混溶的情况下，才能期望尖锐的接口。如果积聚有利于挥发性最小的成分的中心浓度（偶然地是最密集的），则可能会出现弥散界面。在这种结构中产生的组成梯度可能会抑制对流。目前，有两条证据表明冰巨头内饰中可能的氢气不混溶。首先是由实验性氢临界曲线的粗滤出$ \ sim 3 $ GPA引起的（Bali etal。2013）。尽管天王星和海王星也可能“脏”，但获得了包含硅酸盐的不纯系统的数据。当前的AB始于模型不同意（Soubiran＆Militzer 2015），尽管很难以必要的精度从第一原理量子力学中建模氢和水。本文概述的冰巨头中的氢气不混溶的第二个论点是引用引力和磁场的推理。尽管仍然缺乏共识，但我们在这里检查了不可分割的案件。应用所得的热力学约束时，我们发现具有包含大量水摩尔分数的信封的海王星模型，相对于氢，相对于氢，高达$χ\ gtrsim 0.1 $可以满足观察结果。相比之下，天王星模型似乎需要$χ\ lyssim 0.01 $，可能暗示了完全固定的氢和水。从渐进的氢 - 水解凝结可以提供足够的引力势能，以提供大约十个太阳系寿命的Neptune的当今热流。氢 - 水的混合可能会降低海王星的冷却速率。不同的氢 - 水解状状态可以解释天王星和海王星的不同热流。
Interior models of Uranus and Neptune often assume discrete layers, but sharp interfaces are expected only if major constituents are immiscible. Diffuse interfaces could arise if accretion favored a central concentration of the least volatile constituents (also incidentally the most dense); compositional gradients arising in such a structure would likely inhibit convection. Currently, two lines of evidence suggest possible hydrogen-water immiscibility in ice giant interiors. The first arises from crude extrapolation of the experimental hydrogen-water critical curve to $\sim 3$ GPa (Bali et al. 2013). The data are obtained for an impure system containing silicates, though Uranus and Neptune could also be "dirty." Current ab initio models disagree (Soubiran & Militzer 2015), though hydrogen and water are difficult to model from first-principles quantum mechanics with the necessary precision. The second argument for hydrogen-water immiscibility in ice giants, outlined herein, invokes reasoning about the gravitational and magnetic fields. While consensus remains lacking, here we examine the immiscible case. Applying the resulting thermodynamic constraints, we find that Neptune models with envelopes containing a substantial water mole fraction, as much as $χ\gtrsim 0.1$ relative to hydrogen, can satisfy observations. In contrast, Uranus models appear to require $χ\lesssim 0.01$, potentially suggestive of fully demixed hydrogen and water. Enough gravitational potential energy would be available from gradual hydrogen-water demixing, to supply Neptune's present-day heatflow for roughly ten solar system lifetimes. Hydrogen-water demixing could slow Neptune's cooling rate by an order of magnitude; different hydrogen-water demixing states could account for the different heatflows of Uranus and Neptune.
