论文标题
地球的随机增生
Stochastic accretion of the Earth
论文作者
论文摘要
相对于软骨陨石（其可能的构建块），地球耗尽了挥发性元素。这种耗竭的程度随着凝结温度的降低而增加，并且与任何软骨液不同的累积正态分布近似。然而，占据分布的中端的中度挥发性元素具有软骨同位素比，与部分蒸发/凝结所预期的相反。在这里，我们通过使用N体模拟来调和这些观察结果，表明地球从许多前体体中随机积聚，其可变组合物反映了它们形成的温度。仅当原始地球很小时，撞击引起的大气损失才有效，并且在此之后积聚的元素保持接近的同位素比率。当地球至胚胎大小的身体的初始温度通过磁盘积聚速率（1.08 $ \ pm $ 0.17）$ \ times $ 10 $^{ - 7} $ solar Masses/yr时，地球的成分将被复制。该模型意味着与地球的辐射挥发性耗尽年龄一致，在$ \ sim $ 1 MYR内的组成和快速行星形成中的地中心体梯度。
Earth is depleted in volatile elements relative to chondritic meteorites, its possible building blocks. The extent of this depletion increases with decreasing condensation temperature, and is approximated by a cumulative normal distribution, unlike that in any chondrite. However, moderately volatile elements, occupying the mid-range of the distribution, have chondritic isotope ratios, contrary to that expected from loss by partial vaporisation/condensation. Here we reconcile these observations by showing, using N-body simulations, that Earth accreted stochastically from many precursor bodies whose variable compositions reflect the temperatures at which they formed. Impact-induced atmospheric loss was efficient only when the proto-Earth was small, and elements that accreted thereafter retain near-chondritic isotope ratios. Earth's composition is reproduced when initial temperatures of planetesimal- to embryo-sized bodies are set by disk accretion rates of (1.08 $\pm$ 0.17) $\times$ 10$^{-7}$ solar masses/yr, although they may be perturbed by $^{26}$Al heating on bodies formed at different times. The model implies a heliocentric gradient in composition and rapid planetesimal formation within $\sim$ 1 Myr, in accord with radiometric volatile depletion ages of Earth.
