High-order gravity field of differentially rotating Uranus and Neptune models

Abstract:

Less is known about the internal structure and composition of Uranus and Neptune than their classification as ice giants might suggest it is [1]. One of the surprisingly poorly constrained but important parameters for inference of internal structure are their rotation rates [2]. Different possible solid body rotation rates have been shown to yield different moment of inertia [3] and static Love number k22 values for the Neptune-Triton system [4].

Here we expand on our former work and investigate the possibility to use the high-order gravitational harmonics J6-J10 as a diagnostic tool of underlying solid body rotation rates. Methodically, we assume differential rotation on cylinders, which is consistent with observed wind speeds up to mid-latitudes [1]. We apply both the accurate CMS and the faster ToF7 method to calculate the even harmonics J2n.

Measurement of high-order gravitational harmonics would require an orbiting spacecraft similar to Juno at Jupiter [5].

[1] Helled, Nettelmann, Guillot, Sp. Sci. Rev. 2020
[2] Helled, Anderson, Schubert, Icarus 210:446, 2010
[3] Nettelmann, Helled, Fortney, Redmer, Pl. Sp. Sci. 77:143, 2013
[4] Nettelmann, Poster EPSC-DPS 2019
[5] Bolton, Lunine, Stevenson, et al., Sp. Sci. Rev. 213:5, 2017