Enhanced atmospheric loss on protoplanets at the giant impact phase in the presence of oceans
Enhanced atmospheric loss on protoplanets at the giant impact phase in the presence of oceans
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DOI：
10.1038/nature03360
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发表时间：
2005-02-24
期刊：
影响因子：
64.8
通讯作者：
Abe, Y
中科院分区：
文献类型：
--
作者：
Genda, H;Abe, Y
金星和地球的大气成分明显不同，金星大气中的Ar-36含量是地球大气的50倍。太阳风对地球和金星行星形成物质的不同影响已经被提出来解释大气成分的一些差异（2，3），但成分差异的原因尚未完全解决。在这里，我们提出，在巨大的影响阶段，在原行星表面的海洋的存在或不存在可能决定了其随后的大气量和成分。使用数值模拟，我们表明，海洋的存在显着提高了巨大的影响，由于两个效果：蒸发的海洋，和较低的冲击阻抗的海洋相比，地面的大气损失。地球轨道附近的原行星应该有海洋，而金星轨道附近的原行星则没有，因此我们认为富含稀有气体的原大气残留在金星上，但在地球上没有。我们提出的机制解释了金星和地球大气中氩、氪和氙含量的差异，但大部分氖必须在稍后从两颗行星的大气中逃逸，以产生观测到的氖与氩的比例。
The atmospheric compositions of Venus and Earth differ significantly, with the venusian atmosphere containing about 50 times as much Ar-36 as the atmosphere on Earth(1). The different effects of the solar wind on planet-forming materials for Earth and Venus have been proposed to account for some of this difference in atmospheric composition(2,3), but the cause of the compositional difference has not yet been fully resolved. Here we propose that the absence or presence of an ocean at the surface of a protoplanet during the giant impact phase could have determined its subsequent atmospheric amount and composition. Using numerical simulations, we demonstrate that the presence of an ocean significantly enhances the loss of atmosphere during a giant impact owing to two effects: evaporation of the ocean, and lower shock impedance of the ocean compared to the ground. Protoplanets near Earth's orbit are expected to have had oceans, whereas those near Venus' orbit are not, and we therefore suggest that remnants of the noble-gas rich proto-atmosphere survived on Venus, but not on Earth. Our proposed mechanism explains differences in the atmospheric contents of argon, krypton and xenon on Venus and Earth, but most of the neon must have escaped from both planets' atmospheres later to yield the observed ratio of neon to argon.