title: Opacity and conductivity measurements in noble gases at conditions of planetary and stellar interiors.
abstract: 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.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015; School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom; Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh EH9 3FD, United Kingdom; Departamento de Geociencias, Universidad de Los Andes, Bogotá DC, Colombia; Department of Mathematics, Howard University, Washington, DC 20059; stewartmcwilliams@gmail.com.
authors.forename: R Stewart
authors.initials: RS
authors.lastname: McWilliams
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015;
authors.forename: D Allen
authors.initials: DA
authors.lastname: Dalton
authors.affiliation: Deutsches Elektronen-Synchrotron Photon Science, 22607 Hamburg, Germany;
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Konôpková
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015; Department of Mathematics, Howard University, Washington, DC 20059;
authors.forename: Mohammad F
authors.initials: MF
authors.lastname: Mahmood
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015; Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China.
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Goncharov
keywords: extreme conditions; giant planet; rare gases; warm dense matter; white dwarf