The formation and evolution of Mars: Composition and early surface environment

我在读博士期间发表了两篇论文。第一篇论文是关于结合陨石研究和N体模拟结果的同位素数据，以进一步约束行星形成模型。我们的团队发现，为了重现地球和火星之间的同位素差异，无论我们采用的N体模拟动力学模型如何，初始固体盘从顽火辉石球粒陨石到普通球粒陨石的成分变化必须发生在距离太阳约1.3 Au的位置。这项研究开启了将陨石研究与计算模拟数据相结合来研究行星形成的大门。我的第二篇论文重点是在一次巨大撞击后口述火星早期的表面环境。我们的团队将光滑粒子流体动力学（SPH）模拟与分析理论相结合，以计算谷神星大小的撞击与早期火星之间的巨大撞击是否足以改变火星早期的表面环境。这种巨大的撞击很可能发生在4480 Ma之前。我们发现，在巨大的撞击后，大约3巴的氢气（H2）形成。一个厚厚的H2大气层可能是触发生命的一个重要来源，因为它保持了一个有利于生物前化学的还原环境。然而，由于年轻太阳的活跃，如此厚的H2大气不太可能存活超过2000万年。因此，我们得出结论，在这次晚期的巨大撞击之后，火星上很难出现生命。这是一项关于在火星上寻找外星生命的可能性的指示性研究。

I published two papers during my PhD study. The first paper is about combining isotopic data from meteoritic study and N-body simulation results to further constrain planet formation models. Our team found that in order to reproduce the isotopic differences between Earth and Mars, a compositional change of the initial solid disk from enstatite chondrite to ordinary chondrite have to occur at around 1.3 AU from the Sun, regardless of the dynamical models we adopted for the N-body simulations. This study opens the door of combining meteoritic studies with computational simulation data to study planet formation.My second paper focuses on dictating the early surface environment on Mars after a single giant impact. Our team combined Smooth particle hydrodynamic (SPH) simulations with analytical theory to calculate whether a giant impact between a Ceres-sized impact and the early Mars is sufficient in changing the early surface environment on Mars. Such giant impact is likely to have occurred no later than 4480 Ma. We found that after the giant impact, about 3 bars of hydrogen (H2) gas is formed. A thick H2 atmosphere could be an important source for triggering life on a planet since it maintains a reducing environment which favorite pre-biotic chemistry. However, such thick H2 atmosphere is unlikely to survive more than 20 Myr, due to the active young Sun. Hence we concluded that it is difficult for life to emerge on Mars after this late giant impact. This is an indicative research on the possibility of searching for extraterrestrial life on Mars.