Explaining the low luminosity of Uranus: a self-consistent thermal and structural evolution
Explaining the low luminosity of Uranus: a self-consistent thermal and structural evolution
复制标题
解释天王星的低光度：自洽的热和结构演化
DOI：
10.1051/0004-6361/201936588
复制
发表时间：
2019
影响因子：
6.5
通讯作者：
R. Helled
中科院分区：
文献类型：
--
作者：
A. Vazan;R. Helled
天王星的低光度是行星科学长期面临的挑战。简单的绝热模型与测量的光度不一致，这表明天王星是非绝热的，因为它有热边界层和/或传导区域。一个渐进的成分分布作为一个热边界，以抑制对流和减缓内部冷却。在这里，我们调查是否在天王星内部深处的成分梯度可以解释其低光度，所需的成分梯度，以及它是否是稳定的对流混合的时间尺度上的几十亿年。我们改变了行星的原始成分分布和初始能量预算，并选择了适合天王星目前测量的属性（半径，光度和惯性矩）的模型。我们提出了几种替代的非绝热的内部结构，适合天王星的测量。我们发现对流混合仅限于天王星内部，成分梯度是稳定的，足以解释其目前的光度。因此，天王星的内部可能仍然非常热，尽管它的光度很低。稳定的成分梯度也表明天王星目前的内部结构与其原始结构相似。此外，我们认为，天王星的初始能量含量不能大于其形成（吸积）能量的20%。我们还发现，内部是冰和岩石的混合物，而不是分离的冰和岩石外壳，这与测量结果一致，表明天王星可能没有“分化”。我们的模型可以解释天王星的光度，它们也与其富含金属的大气层和磁场产生位置的预测相一致。
The low luminosity of Uranus is a long-standing challenge in planetary science. Simple adiabatic models are inconsistent with the measured luminosity, which indicates that Uranus is non-adiabatic because it has thermal boundary layers and/or conductive regions. A gradual composition distribution acts as a thermal boundary to suppress convection and slow down the internal cooling. Here we investigate whether composition gradients in the deep interior of Uranus can explain its low luminosity, the required composition gradient, and whether it is stable for convective mixing on a timescale of some billion years. We varied the primordial composition distribution and the initial energy budget of the planet, and chose the models that fit the currently measured properties (radius, luminosity, and moment of inertia) of Uranus. We present several alternative non-adiabatic internal structures that fit the Uranus measurements. We found that convective mixing is limited to the interior of Uranus, and a composition gradient is stable and sufficient to explain its current luminosity. As a result, the interior of Uranus might still be very hot, in spite of its low luminosity. The stable composition gradient also indicates that the current internal structure of Uranus is similar to its primordial structure. Moreover, we suggest that the initial energy content of Uranus cannot be greater than 20% of its formation (accretion) energy. We also find that an interior with a mixture of ice and rock, rather than separated ice and rock shells, is consistent with measurements, suggesting that Uranus might not be “differentiated”. Our models can explain the luminosity of Uranus, and they are also consistent with its metal-rich atmosphere and with the predictions for the location where its magnetic field is generated.
影响因子：
3.2
作者：
Redmer, Ronald;Mattsson, Thomas R.;French, Martin
通讯作者：
French, Martin