One-dimensional convective thermal evolution calculation using a modified mixing length theory: Application to Saturnian icy satellites
One-dimensional convective thermal evolution calculation using a modified mixing length theory: Application to Saturnian icy satellites
复制标题
使用修正的混合长度理论的一维对流热演化计算：在土星冰卫星上的应用
DOI：
10.1002/2017je005404
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
S.
中科院分区：
文献类型：
--
作者：
Kamata;S.
固态热对流在固态行星体的热演化中起着重要作用。求解考虑对流的热演化方程系统需要2-D或3-D建模，导致计算成本很高。基于混合长度理论（MLT）的一维计算方案需要低得多的计算成本，并且适合于参数研究。MLT方案的一个主要问题是由于缺乏与高维方案的详细比较，其精度。在这项研究中，我量化的准确性，通过比较1-D MLT和3-D数值方案获得的热剖面。为了提高精度，我提出了一个新的定义的混合长度（l），这是一个参数控制的热传输效率，由于对流，底部加热对流层。采用这种新的定义l，我调查的土星冰冷的卫星，土卫四和土卫二，在各种参数条件下的热演化。计算结果表明，地球物理分析表明，每颗卫星需要几十GW的热量才能拥有一个厚厚的全球地下海洋。尽管土卫四的冰的参考粘度和土卫四海洋的氨含量需要非常高，但动力学潮汐可能能够解释这么多的热量。否则，土卫四中的厚的全球海洋就无法维持，这意味着它的外壳并不处于最小应力状态。
Solid‐state thermal convection plays a major role in the thermal evolution of solid planetary bodies. Solving the equation system for thermal evolution considering convection requires 2‐D or 3‐D modeling, resulting in large calculation costs. A 1‐D calculation scheme based on mixing length theory (MLT) requires a much lower calculation cost and is suitable for parameter studies. A major concern for the MLT scheme is its accuracy due to a lack of detailed comparisons with higher dimensional schemes. In this study, I quantify its accuracy via comparisons of thermal profiles obtained by 1‐D MLT and 3‐D numerical schemes. To improve the accuracy, I propose a new definition of the mixing length (l), which is a parameter controlling the efficiency of heat transportation due to convection, for a bottom‐heated convective layer. Adopting this new definition ofl, I investigate the thermal evolution of Saturnian icy satellites, Dione and Enceladus, under a wide variety of parameter conditions. Calculation results indicate that each satellite requires several tens of GW of heat to possess a thick global subsurface ocean suggested from geophysical analyses. Dynamical tides may be able to account for such an amount of heat, though the reference viscosity of Dione's ice and the ammonia content of Dione's ocean need to be very high. Otherwise, a thick global ocean in Dione cannot be maintained, implying that its shell is not in a minimum stress state.