Benchmarking the ab initio hydrogen equations of state for the interior structure of Jupiter

Abstract

As Juno is presently measuring Jupiter's gravitational moments to unprecedented accuracy, models for the interior structure of the planet are putted to the test. While equations of state based on first principles or ab initio simulations have been available and used for the two most abundant elements constituting the envelope, hydrogen and helium, significant discrepancies remain regarding the predictions of the inner structure of Jupiter. The differences are severe enough to clutter the analysis of Juno's data and even cast doubts on the usefulness of these computationally expensive EOSs for the modeling of the interior of Jupiter and exoplanets at large. Using our newly developed equations of state for hydrogen and helium, we asses the ab initio equations of state currently available and establish their efficiency at predicting the interior structure of Jupiter in a two-layers model. By adjusting our free energy parameterization to reproduce previous ab initio EOS behavior, we identify the source of the disagreement previously reported for the interior structure of Jupiter. We further point to area where care should be taken when building EOS for the modeling of giant planets. This concerns the interpolation between the ab initio results and the physical models used to cover the low density range as well as the interpolation of the {\sl ab initio} simulation results at high densities. This sensitivity falls well within the uncertainties of the ab initio simulations. This suggests that hydrogen EOS should be carefully benchmarked using a simple planetary model before being used in the more advanced planetary models needed to interpret the Juno data. We finally provide an updated version of our ab initio hydrogen EOS recently published.