Session T16: Town Hall Meeting: Materials Physics at Gigabar Pressures

Wednesday, March 12, 2008

Developments in laboratory techniques, combining Megajoule-lasers with dynamic compression methods and diamond-anvil cells, extend the range of high-pressure experiments from the Megabar to the Gigabar regime. Materials could be compressed ~100-fold, with prospects of new correlation phenomena being uncovered. First-principles theory will be tested to far more extreme conditions than previously possible. The feasibility of such experiments has been demonstrated, with current work documenting the metallization of liquid diamond at TPa pressures and of He at 12-fold compression over liquid density ($\sim$104 STP density). Shock pressures to the 10 TPa (100 Mbar) regime have been achieved in the laboratory for the first time. Such capabilities allow new questions to be addressed, such as: What is a solid at TPa (tens of Mbar) pressures? What are the properties of hydrogen atoms compressed to the de Broglie wavelength? What is the nature of the chemical bond at Gbar pressures? How do material properties determine the evolution of exoplanets and brown dwarfs, and what does this reveal about the origins of planets?   

Wednesday, March 12, 2008

The understanding of structures of massive planets such as Jupiter and somewhat lower mass planets such as Uranus can help us tackle some of the central questions in planetary science, such as whether and how planets form. On a decadal timescale, NASA is spending billions of dollars on missions devoted to answering such questions. A crucial part of this understanding is the properties of materials under extreme conditions. Typical conditions inside Jupiter are megabars and ten thousand kelvin, accessible in lab experiment and through simulation. Typical materials are cosmically abundant hydrogen, helium, oxygen, carbon and nitrogen (in appropriate mixtures) and also Earthlike ("rock" and iron). Equation of state, including slopes of isentropes, etc, phase diagrams and transport properties (especially electrical conductivity) are of particular interest. I will describe some of the outstanding unsolved problems for planets, including extrasolar planets more massive than Jupiter.