Laboratory experiments to study warm dense matter and planetary interior structures*

Understanding the properties of Warm Dense Matter (WDM)—the elusive state of matter between hot solids and strongly correlated cold plasmas—is one of the grand challenges of High Energy Density (HED) science. At the extreme density and temperature conditions characteristic of WDM (tens of g/cc and thousands of degrees K), matter exhibits unique properties that reflect how compression and thermal pressure cause the interatomic spacing to decrease and quantum effects to start dominating material behavior, resulting in fundamentally different transport, chemical, and mechanical material properties. Structural and electronic phase transformations also induce dramatic changes in the physico-chemical properties. One of the most fascinating manifestations of WDM occurs within planetary interiors. The discovery of a large number of extrasolar planets, many of which exhibit mass-radius values very different from the planets in the Solar System, has shifted our perception of the Solar System as a prototypical star-planets configuration and has made the study of matter at extreme conditions a necessary link between materials and planetary science. Studying WDM then assumes the double purpose of enhancing the fundamental understating of this exotic state of matter, as well as of providing critical information on density and material properties needed to understand planetary bodies.

Laser-driven dynamic compression techniques enables recreating in the laboratory extreme conditions for a few nanoseconds, giving us a unique opportunity to experimentally probe material properties at the relevant pressures and temperatures. Ultra-fast x-ray and optical diagnostics document in-situ solid-solid phase transitions, melting and metallization, among other material properties.

These techniques are used to characterize the properties and phase transitions of a wide range of elements and compounds relevant to planetary science. Among others, formation of superionic water ice at the conditions existing within Uranus and Neptune, as well as phase transitions in iron and iron oxides at the ultra-high pressures expected in 5 Earth masses terrestrial exoplanets.