Internal Structure Of Giant Planets Research Articles

Partially Diffusive Helium-Silica Compound under High Pressure

Helium is the second most abundant element in the universe, and together with silica, they are important components of giant planets. Exploring the reactivity and state of helium and silica under high pressure is crucial for understanding of the evolution and internal structure of giant planets. Here, using first-principles calculations and crystal structure predictions, we identify four stable phases of a helium-silica compound with seven/eight-coordinated silicon atoms at pressure of 600–4000 GPa, corresponding to the interior condition of the outer planets in the solar system. The density of HeSiO2 agrees with current structure models of the planets. This helium-silica compound exhibits a superionic-like helium diffusive state under the high-pressure and high-temperature conditions along the isentropes of Saturn, a metallic fluid state in Jupiter, and a solid state in the deep interiors of Uranus and Neptune. These results show that helium may affect the erosion of the rocky core in giant planets and may help to form a diluted core region, which not only highlight the reactivity of helium under high pressure but also provide evidence helpful for building more sophisticated interior models of giant planets.

Low- and high-order gravitational harmonics of rigidly rotating Jupiter

The Juno Orbiter has provided improved estimates of the even gravitational harmonics J2 to J8 of Jupiter. To compute higher-order moments, new methods such as the Concentric Maclaurin Spheroids (CMS) method have been developed which surpass the so far commonly used Theory of Figures (ToF) method in accuracy. This progress rises the question whether ToF can still provide a useful service for deriving the internal structure of giant planets in the Solar system. In this paper, I apply both the ToF and the CMS method to compare results for polytropic Jupiter and for the physical equation of state H/He-REOS.3 based models. An accuracy in the computed values of J2 and J4 of 0.1% is found to be sufficient in order to obtain the core mass safely within 0.5 Mearth numerical accuracy and the atmospheric metallicity within about 0.0004. ToF to 4th order provides that accuracy, while ToF to 3rd order does not for J4. Furthermore, I find that the assumption of rigid rotation yields J6 and J8 values in agreement with the current Juno estimates, and that higher order terms (J10 to J18) deviate by about 10% from predictions by polytropic models. This work suggests that ToF4 can still be applied to infer the deep internal structure, and that the zonal winds on Jupiter reach less deep than 0.9 RJup.