Formation of diamonds in laser-compressed hydrocarbons at planetary interior conditions
Formation of diamonds in laser-compressed hydrocarbons at planetary interior conditions
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DOI：
10.1038/s41550-017-0219-9
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发表时间：
2017-09-01
期刊：
影响因子：
14.1
通讯作者：
Falcone, R. W.
中科院分区：
文献类型：
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作者：
Kraus, D.;Vorberger, J.;Falcone, R. W.
碳氢化合物反应和金刚石沉淀对海王星和天王星等冰冷巨行星的内部结构和演化的影响已经讨论了三十多年。在这些天体内部，简单的碳氢化合物，如甲烷，在大气中含量很高（2），被认为经历了结构转变（3，4），从更深层释放出氢，并可能导致致密的分层核心（5-7）。事实上，从表面到核心，天王星和海王星的等熵线相交的温度-压力制度，其中甲烷首先转化为碳氢化合物聚合物的混合物，而在更深层，相分离成金刚石和氢是可能的。在这里，我们展示了通过聚苯乙烯（C8 H8）n样品的原位X射线衍射获得的这种相分离过程的实验证据，这些样品动态压缩到150 GPa和5，000 K左右的条件;这些条件类似于海王星和天王星表面以下约10，000 km的环境（9）。我们的研究结果证明了启动碳氢分离的高压的必要性（3），并暗示金刚石沉淀可能需要大约十倍于先前通过静态压缩实验所指示的压力（4，8，10）。我们的研究结果将为含碳系外行星的质量半径关系提供信息（11），为它们的内层结构提供约束，并改进天王星和海王星的演化模型，其中碳氢分离可能影响对流热传输（7）。
The effects of hydrocarbon reactions and diamond precipitation on the internal structure and evolution of icy giant planets such as Neptune and Uranus have been discussed for more than three decades(1). Inside these celestial bodies, simple hydrocarbons such as methane, which are highly abundant in the atmospheres(2), are believed to undergo structural transitions(3,4) that release hydrogen from deeper layers and may lead to compact stratified cores(5-7). Indeed, from the surface towards the core, the isentropes of Uranus and Neptune intersect a temperature-pressure regime in which methane first transforms into a mixture of hydrocarbon polymers8, whereas, in deeper layers, a phase separation into diamond and hydrogen may be possible. Here we show experimental evidence for this phase separation process obtained by in situ X-ray diffraction from polystyrene (C8H8)n samples dynamically compressed to conditions around 150 GPa and 5,000 K; these conditions resemble the environment around 10,000 km below the surfaces of Neptune and Uranus(9). Our findings demonstrate the necessity of high pressures for initiating carbon-hydrogen separation(3) and imply that diamond precipitation may require pressures about ten times as high as previously indicated by static compression experiments(4,8,10). Our results will inform mass-radius relationships of carbon-bearing exoplanets(11), provide constraints for their internal layer structure and improve evolutionary models of Uranus and Neptune, in which carbon-hydrogen separation could influence the convective heat transport(7).