The curious case of Mars’ formation
The curious case of Mars’ formation
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DOI：
10.1051/0004-6361/201833148
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发表时间：
2018-06
影响因子：
6.5
通讯作者：
J. Woo;R. Brasser;S. Matsumura;S. Mojzsis;S. Ida
中科院分区：
文献类型：
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作者：
J. Woo;R. Brasser;S. Matsumura;S. Mojzsis;S. Ida
行星形成的动力学模型加上火星陨石的宇宙化学数据表明，火星的同位素组成与地球不同。形成模型与陨石数据的协调要求火星距离太阳的距离比目前的位置更远。在这里，我们通过比较两个 N 体行星形成模型的输出来更详细地评估这种成分差异。第一个行星形成模型模拟了所谓的“经典”情况，其中木星和土星保持在当前轨道上。我们将这些结果与另一个基于“大航向”的模型进行比较，其中木星和土星穿过原始小行星带迁移。我们对地球和火星中组装的球粒陨石的平均比例的估计假设初始固体盘仅由内部区域的顽火辉石球粒陨石成分来源和外部区域的普通球粒陨石组成。这些分析的结果表明，这两个模型都倾向于产生吸积区重叠的地球和火星的类似物。经典案例在形成火星方面表现更好，其记录的成分（29-68% 顽火辉石球粒陨石加上 32-67% 普通球粒陨石）尽管火星类似物通常质量太大。然而，如果我们考虑到火星类似物的质量限制，经典模型的效果并不会更好。我们还根据Grand Tack模拟进一步计算了火星地幔中17O、50Ti、54Cr、142Nd、64Ni和92Mo的同位素组成。我们发现，计算出的火星地幔中所有上述元素的同位素组成与测量值是可以匹配的，但由此产生的不确定性太大，无法很好地限制火星早期的动力学演化和诞生地。
Dynamical models of planet formation coupled with cosmochemical data from martian meteorites show that Mars’ isotopic composition is distinct from that of Earth. Reconciliation of formation models with meteorite data require that Mars grew further from the Sun than its present position. Here, we evaluate this compositional difference in more detail by comparing output from twoN-body planet formation models. The first of these planet formation models simulates what is termed the “Classical” case wherein Jupiter and Saturn are kept in their current orbits. We compare these results with another model based on the “Grand Tack”, in which Jupiter and Saturn migrate through the primordial asteroid belt. Our estimate of the average fraction of chondrite assembled into Earth and Mars assumes that the initial solid disk consists of only sources of enstatite chondrite composition in the inner region, and ordinary chondrite in the outer region. Results of these analyses show that both models tend to yield Earth and Mars analogues whose accretion zones overlap. The Classical case fares better in forming Mars with its documented composition (29–68% enstatite chondrite plus 32–67% ordinary chondrite) though the Mars analogues are generally too massive. However, if we include the restriction of mass on the Mars analogues, the Classical model does not work better. We also further calculate the isotopic composition of17O,50Ti,54Cr,142Nd,64Ni, and92Mo in the martian mantle from the Grand Tack simulations. We find that it is possible to match the calculated isotopic composition of all the above elements in Mars’ mantle with their measured values, but the resulting uncertainties are too large to place good restriction on the early dynamical evolution and birth place of Mars.