THE ORIGIN OF THE MOON AND THE SINGLE-IMPACT HYPOTHESIS .3.
THE ORIGIN OF THE MOON AND THE SINGLE-IMPACT HYPOTHESIS .3.
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DOI：
10.1016/0019-1035(89)90129-2
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发表时间：
1989-09-01
期刊：
影响因子：
3.2
通讯作者：
MELOSH, HJ
中科院分区：
文献类型：
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作者：
BENZ, W;CAMERON, AGW;MELOSH, HJ
在本系列的前几篇论文中，光滑粒子流体动力学方法（SPH）已经被用来探索可能导致月球形成的主要行星碰撞的条件。在论文II（W. Benz，W.L.斯莱特里和A.G.W.卡梅隆1987，Icarus 71，30-45），发现当撞击器与原生地球的质量比为0.136时获得最佳条件。在本文中，我们调查的重要性，状态方程的最佳情况下运行几次，并改变状态方程和其他相关参数。比较的两个状态方程是Tillotson（在以前的论文中使用）和CHART D/CSQ ANEOS。由于这些状态方程的差异，包括不同类型的岩石被用于与每个相关联的事实，不可能准备在每个方面都可以比较的初始行星模型，因此需要几个不同的模拟，其中不同的行星参数在状态方程之间匹配。我们还使用了SPH代码的新版本。结果再次证实了先前的主要结论：碰撞在轨道上产生了一个岩石物质盘，其中大部分物质来自撞击物体。这些结果表明，状态方程并不是确定投入轨道的物质数量的关键因素。这证实了论文II的结论，即引力力矩，而不是压力梯度，注入轨道质量。然而，这种质量在轨道上的分布方式受到状态方程和岩石材料选择的影响，对于相同的撞击参数，花岗岩的Tillotson方程给出的留在轨道上的粒子的平均轨道半径略大于ANEOS纯橄榄岩。我们还发现，相比纸二，在所有随后的情况下，新的SPH代码导致一个稍微不扩展的月前吸积盘。我们认为这是由于内核采用了新的形状。进行了一些额外的计算，以测试增加影响参数对计算的影响，其他参数保持不变。这样做的动机是太阳潮汐会随着时间的推移而减少地月角动量。碰撞的角动量增加6%会增加轨道中不含铁的物质的数量及其平均轨道半径，但更多的是增加轨道中铁的数量（铁的平均轨道半径很小）。被摧毁的撞击物体的碎片往往会形成一个直的旋转杆，这在传递角动量方面非常有效。如果靠近棒末端的物质延伸到罗氏瓣之外，它可能会因重力聚集而变得不稳定。
In previous papers in this series the smoothed particle hydrodynamics method (SPH) has been used to explore the conditions in which a major planetary collision may have been responsible for the formation of the Moon. In Paper II (W. Benz, W.L. Slattery, and A.G.W. Cameron 1987, Icarus 71, 30–45) it was found that the optimum conditions were obtained when the mass ratio of the impactor to the protoearth was 0.136. In the present paper we investigate the importance of the equation of state by running this optimum case several times and varying the equation of state and other related parameters. The two equations of state compared are the Tillotson (used in the previous papers) and the CHART D/CSQ ANEOS. Because of differences in these equations of state, including the fact that different types of rocks were used in association with each, it was not possible to prepare initial planetary models that were comparable in every respect, so several different simulations were necessary in which different planetary parameters were matched between the equations of state. We also used a new version of the SPH code. The results reaffirmed the previous principal conclusions: the collisions produced a disk of rocky material in orbit, with most of the material derived from the impacting object. These results indicate that the equation of state is not a critical factor in determining the amount of material thrown into orbit. This confirms the conclusions of Paper II that gravitational torques, and not pressure gradients, inject the orbiting mass. However, the way this mass is distributed in orbit is affected by the equation of state and the choice of rock material, the Tillotson equation for granite giving a slightly larger mean orbital radius for the particles left in orbit than the ANEOS dunite for the same impact parameter. We also find, compared to Paper II, that in all subsequent cases the new SPH code leads to a slightly less extended prelunar accretion disk. We think this is due to the new shape adopted for the kernel. A few additional calculations were made to test the effects of increasing the impact parameter on the calculations, other parameters remaining unchanged. The motivation for this was that solar tides will have reduced the Earth-Moon angular momentum somewhat over the course of time. An increment of 6% in the angular momentum of the collision increases the amount of iron-free material in orbit and its mean orbital radius, but more than that leaves increasing amounts of iron in orbit (the iron has a small mean orbital radius). The debris from the destroyed impacting object tends to form a straight rotating bar which is very effective in transferring angular momentum. If the material near the end of the bar extends well beyond the Roche lobe, it may become unstable against gravitational clumping.