The feeding zones of terrestrial planets and insights into Moon formation
The feeding zones of terrestrial planets and insights into Moon formation
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DOI：
10.1016/j.icarus.2015.01.013
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发表时间：
2015-05-15
期刊：
影响因子：
3.2
通讯作者：
Cowan, Nicolas B.
中科院分区：
文献类型：
--
作者：
Kaib, Nathan A.;Cowan, Nicolas B.
类地行星形成的最后阶段包括几百个近似月球质量的天体吸积成几个类地行星。这最后一个阶段是随机的，因此很难预测原始微行星盘的哪些部分对我们的每个类地行星做出了贡献。在这里，我们提出了一套广泛的类地行星形成模拟，允许定量分析这一过程。虽然有一个行星的位置和其组成的星子的初始半长轴之间的一般相关性，我们同意以前的研究，金星，地球和火星类似物有重叠，随机喂养区。我们将进食区宽度Aa量化为构成最终行星的行星胚胎和星子的初始半长轴的质量加权标准偏差。在我们的模拟中，行星的进食区的大小与其最终质量或半长轴无关，这表明行星的质量与其波动的库存之间没有系统的趋势。相反，我们发现任何质量大于0.1 M圆的行星的进食区与其形成的初始盘的径向范围大致成比例：Δ α近似为0.25（α（最大）-α（最小）），其中α（最小）和α（最大）是初始小行星盘的内外边缘。这些广泛的随机补给区对月球的起源有着重要的影响，因为经典的假设预测月球应该主要由地球最后一个主要撞击物（忒伊亚）的物质组成，但其同位素组成与地球无法区分。特别是，我们发现，忒伊亚类似物的喂养区是显着更随机比行星类似物。根据我们假设的氧同位素在星子盘内的初始分布，我们发现地球和忒伊亚形成的概率接近5%或更低，其同位素差异等于或小于地球和月球的。事实上，我们预测，每一个行星质量体都应该有一个独特的同位素特征。此外，我们发现缺乏大量的忒伊亚类似物和高速月球形成碰撞，这是最近提出的两种对月球同位素组成的解释。我们的工作表明，仍然没有一个关于月球起源的方案，可以用高概率事件来解释其同位素组成。(C)2015 Elsevier Inc. All rights reserved.
The final stage of terrestrial planet formation consists of several hundred approximately lunar mass bodies accreting into a few terrestrial planets. This final stage is stochastic, making it hard to predict which parts of the original planetesimal disk contributed to each of our terrestrial planets. Here we present an extensive suite of terrestrial planet formation simulations that allows quantitative analysis of this process. Although there is a general correlation between a planet's location and the initial semi-major axes of its constituent planetesimals, we concur with previous studies that Venus, Earth, and Mars analogs have overlapping, stochastic feeding zones. We quantify the feeding zone width, Aa, as the mass-weighted standard deviation of the initial semi-major axes of the planetary embryos and planetesimals that make up the final planet. The size of a planet's feeding zone in our simulations does not correlate with its final mass or semi-major axis, suggesting there is no systematic trend between a planet's mass and its volatile inventory. Instead, we find that the feeding zone of any planet more massive than 0.1 M-circle plus is roughly proportional to the radial extent of the initial disk from which it formed: Delta alpha approximate to 0.25(alpha(max) - alpha(min)), where alpha(min) and alpha(max) are the inner and outer edge of the initial planetesimal disk. These wide stochastic feeding zones have significant consequences for the origin of the Moon, since the canonical scenario predicts the Moon should be primarily composed of material from Earth's last major impactor (Theia), yet its isotopic composition is indistinguishable from Earth. In particular, we find that the feeding zones of Theia analogs are significantly more stochastic than the planetary analogs. Depending on our assumed initial distribution of oxygen isotopes within the planetesimal disk, we find a similar to 5% or less probability that the Earth and Theia will form with an isotopic difference equal to or smaller than the Earth and Moon's. In fact we predict that every planetary mass body should be expected to have a unique isotopic signature. In addition, we find paucities of massive Theia analogs and high velocity Moon-forming collisions, two recently proposed explanations for the Moon's isotopic composition. Our work suggests that there is still no scenario for the Moon's origin that explains its isotopic composition with a high probability event. (C) 2015 Elsevier Inc. All rights reserved.