Recreating planetary cores in the laboratory

Accurate phase diagrams for simple molecular fluids (H₂, H₂O, NH₃ and CH₄) and their constituent elements at temperatures of several thousand Kelvin and pressures of several Mbar are integral to planetary models of the gas giant planets (Jupiter, Saturn, Uranus and Neptune). Experimental data at high pressure has, until recently, been limited to around 1 Mbar. These pressures are usually achieved dynamically with explosives and two-stage light-gas guns, or statically with diamond anvil cells. Current high intensity laser facilities can produce tens of Mbar pressures in these light fluids. This presentation will first describe recent shock compressed Hugoniot data for water at pressures up to 8 Mbar. At Hugoniot pressures near 1 Mbar, water becomes an electronic conductor as observed through the shock front reflectivity. Similar experimental results will be shown for carbon starting from the diamond phase. Reflectivity data reveal diamond metalizes near the Hugoniot pressure of 11 Mbar and is perhaps coincident with the melt transition. To obtain high pressure data very close to planetary isentropes, techniques are being developed to generate off Hugoniot data (lower temperature and higher density than standard Hugoniot track). Two techniques to achieve such high density states (double shock and precompressed samples) have been tested. These techniques and preliminary data from these experiments will be described.