The properties of hydrogen-helium mixtures at Mbar pressures and intermediate temperatures (4000 to 10000 K) are calculated with first-principles molecular dynamics simulations. We determine the equation of state as a function of density, temperature, and composition and, using thermodynamic integration, we estimate the Gibbs free energy of mixing, thereby determining the temperature, at a give...

The obliquity of a planet is the tilt between its equator and orbital plane. Giant planets are expected to form with near-zero obliquities. After formation, some dynamical mechanism must therefore have tilted Saturn up current 26.7{\deg}. This event traditionally thought happened more than 4 Gyrs ago during late planetary migration because crossing resonance spin-axis precession nodal mode Nept...