期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：26
页码：7925-7930
DOI：10.1073/pnas.1421801112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificancePlanets and stars contain matter at extreme pressures and temperatures hidden deep beneath their opaque surfaces. Unable to see these states of matter directly, we instead produce them in laboratory experiments. Here a novel method of studying extreme states in a tabletop experiment is described and applied to common planet- and star-forming materials, the noble gases. Helium, neon, argon, and xenon transform in the experiments from transparent electrical insulators to opaque electrical conductors. In Saturn, rain composed of noble gas becomes conductive as it falls and can form a protective layer around the planetary core that prevents the core from dissolving into surrounding metallic hydrogen. White dwarf stars have unexpectedly opaque helium atmospheres, causing them to age slower than anticipated. The noble gases are elements of broad importance across science and technology and are primary constituents of planetary and stellar atmospheres, where they segregate into droplets or layers that affect the thermal, chemical, and structural evolution of their host body. We have measured the optical properties of noble gases at relevant high pressures and temperatures in the laser-heated diamond anvil cell, observing insulator-to-conductor transformations in dense helium, neon, argon, and xenon at 4,000-15,000 K and pressures of 15-52 GPa. The thermal activation and frequency dependence of conduction reveal an optical character dominated by electrons of low mobility, as in an amorphous semiconductor or poor metal, rather than free electrons as is often assumed for such wide band gap insulators at high temperatures. White dwarf stars having helium outer atmospheres cool slower and may have different color than if atmospheric opacity were controlled by free electrons. Helium rain in Jupiter and Saturn becomes conducting at conditions well correlated with its increased solubility in metallic hydrogen, whereas a deep layer of insulating neon may inhibit core erosion in Saturn.
