Thermal history, core formation and tectonics of Mars

我们建立了一个新的火星早期热历史和吸积过程中金属/硅酸盐分离的数值模型，在该模型中，我们考虑了激波传播、陨石坑挖掘、瞬时陨石坑的均衡反弹和等压核尺寸变化的影响，评估了每一次撞击引起的热扰动。研究表明，在火星吸积后，在岩浆池底部形成的金属斑点的沉降导致了富金属层的形成。然而，由于位于中心的未分化岩心的高粘度，在吸积过程中不会进行岩心形成。为了从数值上追踪火星吸积后富金属层和中心未分化核的重力翻转过程，我们还开发了一个新的计算火星核形成过程的数值程序。结果表明，翻转过程依赖于中心未分化核的粘性结构。如果中央地核的粘度为1023PaS，那么翻转的时间不到107年。这一结果表明，火星的核心形成发生在火星吸积后约20亿年。

We have constructed a new numerical model of early thermal history and metal/silicate separation of Mars during accretion in which we evaluate thermal disturbance due to each impact by taking into account the effects of shock propagation, crater excavation, isostatic rebound of transient crater and change in size of isobaric core. According to this study it is shown that settling of metal blob formed at the bottom of magma pond results in formation of metal rich layer just after accretion of Mars. However, core formation does not proceed during accretion because of high viscosity of undifferentiated core located at the center. To trace numerically gravitational overturn process of metal-rich layer and central undifferentiated core after the accretion of Mars we also developed a new numerical code to calculate core formation process of Mars. It is shown that the overturn process is dependent on the structure of viscosity in the central undifferentiated core. If the viscosity of the central core is 1023 Pa s, time of the overturn is less than 107 years. This result suggests that the core formation of Mars occurs at about 2 billion years after accretion of Mars.