Isotopically distinct terrestrial planets via local accretion
Isotopically distinct terrestrial planets via local accretion
复制标题
通过局部吸积形成同位素不同的类地行星
DOI：
10.1016/j.icarus.2020.114052
复制
发表时间：
2020
期刊：
影响因子：
3.2
通讯作者：
R. Brasser
中科院分区：
文献类型：
--
作者：
J. Mah;R. Brasser
将来自陨石数据的同位素约束与行星形成的动力学模型相结合，证明有利于确定类地行星形成的最佳模型。先前的研究表明，无论是经典模型还是大Tack模型，重现地球和火星不同同位素组成的可能性都非常低。在大塔克模型的框架下，火星在同位素上与地球不同，它必须在非常特殊的条件下形成。在这里，我们使用了一个相当新的、尚未开发的模型——耗尽磁盘模型——进行测试。它的前提是，火星轨道内外的原行星盘中区域的质量已经耗尽，以至于火星留下的物质不足以增长到更大的尺寸。我们的目的是测试地球和火星的不同同位素组成是否是这个模型的自然结果。我们发现类地行星主要是局部吸积物质，并且有足够明显的哺养带。如果在原行星盘的类地行星区域存在一个同位素梯度，那么地球和火星，以及引申开来的金星，就可以有不同的同位素组成。我们的结果表明，太阳系内部的物质很可能没有经历大量的混合，从而使潜在的同位素梯度均匀化，这与Grand Tack模型形成了鲜明对比。Grand Tack模型认为，由于木星迁移带来的物质混合，类地行星的喂养区几乎是相同的。
Combining isotopic constraints from meteorite data with dynamical models of planet formation proves to be advantageous in identifying the best model for terrestrial planet formation. Prior studies have shown that the probability of reproducing the distinct isotopic compositions of the Earth and Mars for both classical and Grand Tack models is very low. In the framework of the Grand Tack model, for Mars to be isotopically different from the Earth, it had to form under very specific conditions. Here, we subjected a fairly new and unexplored model—the depleted disc model—to the test. It presupposes that the region in the inner protoplanetary disc from Mars’ orbit and beyond is depleted in mass such that Mars is left with insufficient material to grow to a larger size. Our aim is to test the whether the distinct isotopic compositions of the Earth and Mars are a natural outcome of this model. We found that the terrestrial planets accrete material mostly locally and have feeding zones that are sufficiently distinct. The Earth and Mars, and by extension, Venus, can have distinct isotopic compositions if there is an isotopic gradient in the terrestrial planet region of the protoplanetary disc. Our results suggest that the material in the inner Solar System most likely did not undergo substantial mixing that homogenised the potential isotopic gradient, in contrast to the Grand Tack model where the feeding zones of the terrestrial planets are nearly identical due to the mixing of material by Jupiter’s migration.