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arXiv 1810.04544astro-ph.EP
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捕获岩石系外行星内部碳化硅的氧化

Capturing the oxidation of silicon carbide in rocky exoplanetary interiors

Kaustubh Hakim, Wim van Westrenen, Carsten Dominik

摘要:

理论模型预测碳化硅在C/O比高于0.65的宿主恒星周围凝结(参见图1)。C/O $_{\mathrm{Sun}}$ = 0.54),此外还对陨石、星际介质和原行星盘进行了观测。因此,从富含碳的耐火材料中产生的岩石系外行星的内部通常被认为含有大量的碳化硅。在这里,我们的目标是研究碳化硅在富含碳的岩石系外行星内部的稳定性,并推导出导致其转变的反应。我们进行了一项高压高温实验,以研究碳化硅层和代表富碳岩石系外行星主体成分的层之间的反应。我们报告的反应导致氧化碳化硅生产石英,石墨,和熔融硅化铁。结合以前的研究,我们表明,为了稳定碳化硅,碳饱和是不够的,和一个完整的还原铁$^{2+}$到铁$^{0}$在行星地幔是必需的,这表明未来的光谱检测的Fe $^{2+}$或Fe $^{3+}$的岩石系外行星的表面将意味着在其内部没有碳化硅。

英文摘要:

Theoretical models predict the condensation of silicon carbide around host stars with C/O ratios higher than 0.65 (cf. C/O$_{\mathrm{Sun}}$ = 0.54), in addition to its observations in meteorites, interstellar medium and protoplanetary disks. Consequently, the interiors of rocky exoplanets born from carbon-enriched refractory material are often assumed to contain large amounts of silicon carbide. Here we aim to investigate the stability of silicon carbide in the interior of carbon-enriched rocky exoplanets and to derive the reaction leading to its transformation. We performed a high-pressure high-temperature experiment to investigate the reaction between a silicon carbide layer and a layer representative of the bulk composition of a carbon-enriched rocky exoplanet. We report the reaction leading to oxidation of silicon carbide producing quartz, graphite, and molten iron silicide. Combined with previous studies, we show that in order to stabilize silicon carbide, carbon saturation is not sufficient, and a complete reduction of Fe$^{2+}$ to Fe$^{0}$ in a planetary mantle is required, suggesting that future spectroscopic detection of Fe$^{2+}$ or Fe$^{3+}$ on the surface of rocky exoplanets would imply the absence of silicon carbide in their interiors.

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