Jupiter's helium rain layer as a laboratory for high pressure physics

The first-principles predictions of the metallization of hydrogen at high pressures is a classic result of quantum statistical physics, as is the associated prediction of hydrogen-helium immiscibility. Although these results are generally accepted on a theoretical basis in the high-pressure limit, laboratory experiments to demarcate the phase separation boundary remain largely impractical. Thus, our best understanding of the hydrogen-helium phase diagram is derived from ab initio density functional theory molecular dynamics (DFT-MD) computational simulations. However, results from current state-of-the-art DFT-MD models are generally incompatible with each other, necessitating empirical data to resolve these differences. In this talk, we construct a framework to use measurements from the Galileo probe mass spectrometer experiment and the Juno spacecraft magnetometer experiment to place empirical constraints on the hydrogen-helium phase diagram using Jupiter's interior as a high-pressure laboratory. We argue that the region in Jupiter's interior where hydrogen and helium phase separate--often called its "helium rain layer"--should be electrically conducting and stable against convection. We then posit that if the helium rain layer is differentially rotating with respect to the background field, then magnetohydrodynamic effects will attenuate non-axisymmetric components of Jupiter's magnetic field, as has been previously suggested to apply to Saturn. We present for the first-time evidence for such an effect on Jupiter using Juno spacecraft data. Finally, we motivate future work on the basis of both understanding the formation history of the Solar System's largest planet, and testing our theories of matter under conditions difficult to replicate in present-era laboratories.