Atmospheric Loss in Giant Impacts Depends on Preimpact Surface Conditions
Atmospheric Loss in Giant Impacts Depends on Preimpact Surface Conditions
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DOI：
10.3847/psj/ad0b16
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发表时间：
2023-09
影响因子：
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通讯作者：
S. Lock;Sarah T. Stewart
中科院分区：
文献类型：
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作者：
S. Lock;Sarah T. Stewart
地球可能在其形成的主要阶段获得了大部分挥发性元素的库存。因此，地球的一些原始大气一定在巨大的撞击中幸存了下来，即行星大小的天体之间的碰撞，这些碰撞主导了吸积的后期阶段。在这里，我们使用一套一维流体动力学模拟和阻抗匹配计算来量化撞击前表面条件(如大气压力和海洋的存在)对巨大撞击期间原行星大气和海洋损失的效率的影响。我们发现，在没有海洋的情况下，更轻、更热、更低气压的大气更容易消失。与没有海洋的情况相比，海洋的存在可以显著提高大气损失的效率，随着大气与海洋的质量比降低，在低损失和高损失之间快速过渡。然而，与之前的想法相反，如果海洋的质量不够大，通常不到大气质量的几倍，海洋的存在也可以减少大气损失。因此，巨大撞击造成的挥发损失对碰撞物体上的表面条件高度敏感。为了将我们的结果与3D碰撞模拟相结合，我们开发了将损失与地面速度和表面条件相关联的比例定律。我们的结果表明，行星的最终不稳定预算严重依赖于它们的前身行星胚胎经历的准确时间和撞击序列，这使得大气特性是高度随机的吸积结果。
Earth likely acquired much of its inventory of volatile elements during the main stage of its formation. Some of Earth’s proto-atmosphere must therefore have survived the giant impacts, collisions between planet-sized bodies, that dominate the latter phases of accretion. Here, we use a suite of 1D hydrodynamic simulations and impedance-match calculations to quantify the effect that preimpact surface conditions (such as atmospheric pressure and the presence of an ocean) have on the efficiency of atmospheric and ocean loss from protoplanets during giant impacts. We find that—in the absence of an ocean—lighter, hotter, and lower-pressure atmospheres are more easily lost. The presence of an ocean can significantly increase the efficiency of atmospheric loss compared to the no-ocean case, with a rapid transition between low- and high-loss regimes as the mass ratio of atmosphere to ocean decreases. However, contrary to previous thinking, the presence of an ocean can also reduce atmospheric loss if the ocean is not sufficiently massive, typically less than a few times the atmospheric mass. Volatile loss due to giant impacts is thus highly sensitive to the surface conditions on the colliding bodies. To allow our results to be combined with 3D impact simulations, we have developed scaling laws that relate loss to the ground velocity and surface conditions. Our results demonstrate that the final volatile budgets of planets are critically dependent on the exact timing and sequence of impacts experienced by their precursor planetary embryos, making atmospheric properties a highly stochastic outcome of accretion.