论文标题
行星岩浆海洋中的对流超出效率：计算流体动力学的见解
Convective outgassing efficiency in planetary magma oceans: insights from computational fluid dynamics
论文作者
论文摘要
通常认为，行星气氛通常是由于冷却岩浆海洋的有效排气而产生的。在此阶段，融化内部剧烈的对流运动被认为会迅速将溶解的挥发物迅速运输到浅深度，它们在表面上散发并破裂。这种有效脱气和大气形成的假设对行星进化具有重要意义，但从未对流体动力学考虑进行测试。然而，在对流循环中，只有有限的岩浆海洋可以到达可能发生挥发物的浅深度，并且大规模循环可能会阻止大量岩浆海洋的体积迅速到达地球表面。因此，我们对PrandTL数量的剧烈2D和3D Rayleigh-Bénard对流进行了计算流体动力学实验，以表征对流液达到浅深度的能力，使挥发物被溶解并提取到大气中。超出效率实质上是对流速度幅度的函数。这允许得出简单的表达式，可以预测超出挥发物的量的时间演变，这是岩浆海洋管理参数的函数。对于合理的情况，在给定的高度剧烈的瞬态阶段中，所有过饱和水所需的时间可能超过岩浆海洋的寿命，从而导致不完整甚至可以忽略不计。此外，分别通过对流的活力和降解深度对岩浆海洋的脱气效率，分别通过对流的活力和降解深度分别导致行星演化路径和导致的表面条件，分别对岩浆海洋脱气效率。总体而言，尽管对流有剧烈的对流，但对于大量参数，对流脱气似乎不如先前想象的那么效率。
Planetary atmospheres are commonly thought to result from the efficient outgassing of cooling magma oceans. During this stage, vigorous convective motions in the molten interior are believed to rapidly transport the dissolved volatiles to shallow depths where they exsolve and burst at the surface. This assumption of efficient degassing and atmosphere formation has important implications for planetary evolution, but has never been tested against fluid dynamics considerations. Yet, during a convective cycle, only a finite fraction of the magma ocean can reach the shallow depths where volatiles exsolution can occur, and a large-scale circulation may prevent a substantial magma ocean volume from rapidly reaching the planetary surface. Therefore, we conducted computational fluid dynamics experiments of vigorous 2D and 3D Rayleigh-Bénard convection at Prandtl number of unity to characterize the ability of the convecting fluid to reach shallow depths at which volatiles are exsolved and extracted to the atmosphere. Outgassing efficiency is essentially a function of the magnitude of the convective velocities. This allows deriving simple expressions to predict the time evolution of the amount of outgassed volatiles as a function of the magma ocean governing parameters. For plausible cases, the time required to exsolve all oversaturated water can exceed the magma ocean lifetime in a given highly vigorous transient stage, leading to incomplete or even negligible outgassing. Furthermore, the planet size and the initial magma ocean water content, through the convective vigor and the exsolution depth, respectively, strongly affect magma oceans degassing efficiency, possibly leading to divergent planetary evolution paths and resulting surface conditions. Overall, despite vigorous convection, for a significant range of parameters, convective degassing appears not as efficient as previously thought.
