Equilibrium Tidal Response of Jupiter: Detectability by Juno

Published in Astrophysical Journal, 2020

Recommended citation: S M Wahl, M Parisi, W M Folkner, W B Hubbard, B Militzer, ApJ, 891, 1, 2020.

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Abstract

An observation of Jupiter’s tidal response is anticipated for the ongoing Juno spacecraft mission. We combine self-consistent, numerical models of Jupiter’s equilibrium tidal response with observed Doppler shifts from the Juno gravity science experiment to test the sensitivity of the spacecraft to tides raised by the Galilean satellites and the Sun. The concentric Maclaurin spheroid (CMS) method finds the equilibrium shape and gravity field of a rotating, liquid planet with the tide raised by a satellite, expanded in Love numbers (k nm ). We present improvements to the CMS theory that eliminate an unphysical center-of-mass offset and study in detail the convergence behavior of the CMS approach. We demonstrate that the dependence of k nm with orbital distance is important when considering the combined tidal response for Jupiter. Conversely, the details of the interior structure have a negligible influence on k nm for models that match the zonal harmonics J 2, J 4, and J 6, already measured to high precision by Juno. As the mission continues, improved coverage of Jupiter’s gravity field at different phases of Io’s orbit is expected to yield an observed value for the degree-two Love number (k 22) and potentially select higher-degree k nm . We present a test of the sensitivity of the Juno Doppler signal to the calculated k nm , which suggests the detectability of k 33, k 42, and k 31, in addition to k 22. A mismatch of a robust Juno observation with the remarkably small range in calculated Io equilibrium, k 22 = 0.58976 ± 0.0001, would indicate a heretofore uncharacterized dynamic contribution to the tides.