Hydrogen and hydrogen-helium mixtures under high pressure. A density functional and molecular dynamics study

Abstract

An experimental observation that requires a theoretical explanation is the large excess energy radiation of the giant planets. For example, Jupiter radiates almost twice the amount of energy it receives from the sun. To explain the excess energy output, R. Smoluchowski invoked phase separation of hydrogen and helium in the interior of Jupiter. Helium droplets nucleate from the heavier phase and sink to the center of the planet releasing gravitational energy. Phase separation is desirable as an explanation for the excess energy radiation of Saturn but not Jupiter. In view of its astrophysical importance, the study of hydrogen at high pressures is one of the key problems in modern physics and astrophysics. For a quantitative understanding of the physics in the interiors of the giant planets it is crucial to go beyond the study of the pure phase. We investigate an astrophysical H-He mixture at Mbar pressures. The inert helium atoms are a major perturbation to the hydrogen system, leading to significantly different structural and electronic properties. We also compute the demixing temperatures for high pressure H-He mixtures and discuss the implications for the interiors of the giant planets. In the following we introduce the reader to a small part of the ''Hydrogen World'' and the disturbance of this world by helium ''intruders'', and we hope to capture some of the fascinating complexity of two ''simple'' systems. (orig.)205 refs.Available from TIB Hannover: RA 831(3281) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman