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arXiv 1909.07560astro-ph.EP
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火星的组成

The composition of Mars

Takashi Yoshizaki, William F. McDonough

摘要:

比较类地行星的组成模型,可以深入了解产生行星尺度相似性和差异的物理化学过程。广泛接受的火星成分模型假设Mn和更多的难熔元素在行星中以Cl球粒陨石的比例存在,包括Fe,Mg和Si,它们与O一起构成火星质量的$>$ 90%。然而,最近我们对太阳光球和陨石组成的理解的改进挑战了CI球粒陨石作为火星模拟物的使用。在这里,我们提出了一个替代模型组成的火星,避免了这样的假设,是基于火星陨石和航天器观测的数据。我们的建模方法以前被应用于预测地球的组成。该模型建立了耐火亲石元素的绝对丰度在散装硅酸盐火星(BSM)在2.26倍高于CI碳质方解石。相对于这一南极组成,火星有一个系统的消耗在中度挥发性亲石元素作为其冷凝温度的函数。鉴于这一发现,我们限制了大量的火星及其核心的亲铁和亲铜元素的丰度。火星波动趋势与其核心中的$ \leq $ 7 wt\% S一致,这明显低于大多数核心模型中假设的水平(即,$ > $ 10重量% S)。此外,在火星的核幔边界的ringwoodite的发生可能有助于分配的O和H到火星的核心。

英文摘要:

Comparing compositional models of the terrestrial planets provides insights into physicochemical processes that produced planet-scale similarities and differences. The widely accepted compositional model for Mars assumes Mn and more refractory elements are in CI chondrite proportions in the planet, including Fe, Mg, and Si, which along with O make up $>$90\% of the mass of Mars. However, recent improvements in our understandings on the composition of the solar photosphere and meteorites challenge the use of CI chondrite as an analog of Mars. Here we present an alternative model composition for Mars that avoids such an assumption and is based on data from Martian meteorites and spacecraft observations. Our modeling method was previously applied to predict the Earth's composition. The model establishes the absolute abundances of refractory lithophile elements in the bulk silicate Mars (BSM) at 2.26 times higher than that in CI carbonaceous chondrites. Relative to this chondritic composition, Mars has a systematic depletion in moderately volatile lithophile elements as a function of their condensation temperatures. Given this finding, we constrain the abundances of siderophile and chalcophile elements in the bulk Mars and its core. The Martian volatility trend is consistent with $ \leq $7 wt\% S in its core, which is significantly lower than that assumed in most core models (i.e., $ > $10 wt\% S). Furthermore, the occurrence of ringwoodite at the Martian core-mantle boundary might have contributed to the partitioning of O and H into the Martian core.

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