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

TL;DR

This paper compares the accuracy of the Theory of Figures and Concentric Maclaurin Spheroids methods in modeling Jupiter's gravitational harmonics, demonstrating ToF4's sufficiency for internal structure inference and insights into Jupiter's zonal winds.

Contribution

It evaluates the applicability of ToF and CMS methods for modeling Jupiter's gravitational field, highlighting ToF4's adequacy and providing insights into Jupiter's internal structure and zonal wind depth.

Findings

ToF4 achieves 0.1% accuracy for J2 and J4.

Rigid rotation assumptions match Juno's J6 and J8 estimates.

Higher order harmonics deviate by about 10% from polytropic models.

Abstract

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.