  Ionic structure of high pressure, high temperature fluids is a challenging
theoretical problem with applications to planetary interiors and fusion
capsules. Here we report a multi-messenger platform using velocimetry and
\textit{in situ} angularly and spectrally resolved X-ray scattering to measure
the thermodynamic conditions and ion structure factor of materials at extreme
pressures. We document the pressure, density, and temperature of shocked
silicon near 100 GPa with uncertainties of 6%, 2%, and 20%, respectively. The
measurements are sufficient to distinguish between and rule out some ion
screening models.
