Planetary science

The predictive capability of QMD simulations allows us to determine the properties of materials subject to planetary interiors conditions. The equation-of-state (EOS) of the planetary materials, specifically the pressure as a function of density, temperature, and composition, are required in order to close the set of hydrostatic equations used in planetary models [1,2].

A large part of the uncertainty in models of Saturn and Jupiter lies in the existence and location an inhomogeneous region where helium separates from hydrogen to form helium rich droplets that fall deeper into the planet due to their larger density. We use first-principles simulations to predict the temperature, as a function of pressure, at which helium becomes insoluble in dense metallic hydrogen [3] and study the impact of helium on the equation of state of hydrogen and the properties of that mixture [4]. The presence of other elements will also modify the properties of hydrogen and their impact at high pressure and temperature is also of interest.
In ice giants such as Uranus and Neptune, the uncertainty in the planetary models comes mainly from the properties of mixtures of water, ammonia and methane (referred to as “ices”) at high pressures and temperatures [5]. Many observables properties of these planets, such as gravitational moments, atmospheric composition and magnetic fields, are thought to be determined by the physical and chemical properties of matter within this ice layer [6]. Of particular interest is the impact of the complex organic chemistry on the fluid properties at these extreme conditions.

[1] D. C. Swift, J. H. Eggert, D. G. Hicks, S. Hamel, K. Caspersen, E. Schwegler, G. W. Collins, N. Nettelmann  and G. J. Ackland Mass-Radius Relationships for Exoplanets. Astro. Phys. J. 744, 59 (2012)

[2] R. G. Kraus, S. T. Stewart, D. C. Swift, C. A. Bolme, R. F. Smith, S. Hamel, B. D. Hammel, D. K. Spaulding, D. G. Hicks, J. H. Eggert, G. W. Collins Shock vaporization of silica and the thermodynamics of planetary impact events. J. Geophys. Research – Planets 117, E09009 (2012)

[3] Morales, MA; Schwegler, E; Ceperley, D; Pierleoni, C; Hamel, S; Caspersen, K. Phase separation in hydrogen-helium mixtures at Mbar pressures. P. Natl. Acad. Sci. USA, 106, 1324-1329, (2009)

[4] S. Hamel, Miguel Morales and Eric Schwegler, Signature of helium segregation in hydrogen-helium mixtures. Phys. Rev. B 84, 165110 (2011)

[5] R. Chau, S. Hamel, and W. J. Nellis Chemical Processes in the Deep Interior of Uranus. Nature Communications, 2, (2011)

[6] M. French; S. Hamel and R. Redmer Dynamical Screening and Ionic Conductivity in Water from Ab Initio Simulations. Phys. Rev. Lett., 107, 185901 (2011)