Ring Seismology of the Ice Giants Uranus and Neptune

TL;DR

This study explores how ring seismology can be used to investigate the interior structures of Uranus and Neptune by predicting where oscillation-induced resonances might be observed in their rings.

Contribution

It provides detailed predictions of normal mode spectra and their potential ring resonances for Uranus and Neptune, aiding future interior modeling and observational efforts.

Findings

Resonances with specific azimuthal orders fall in known rings of Uranus.

Certain f-mode and g-mode resonances are predicted in Neptune's rings.

Identifying these modes could constrain interior models of the ice giants.

Abstract

We assess the prospect of using ring seismology to probe the interiors of the ice giants Uranus and Neptune. We do this by calculating normal mode spectra for different interior models of Uranus and Neptune using the stellar oscillation code GYRE. These spectra provide predictions of where in these planets' ring systems the effects of interior oscillations might be detected. We find that f-mode resonances with azimuthal order $m=2$ or $7 \leq m \leq 19$ fall among the inner rings (6, 5, 4, $\alpha$, and $\beta$) of Uranus, while f-mode resonances with $2 \leq m \leq 12$ fall in the tenuous $\zeta$ ring region. In addition, f-mode resonances with $m=2$ or $6 \leq m \leq 13$ may give azimuthal structure to Neptune's tenuous Galle ring. We also find that g-mode resonances may fall in the middle to outer rings of these planets. Although an orbiter is most likely required to confirm the association between any waves in the rings and planetary normal modes, the diversity of normal mode spectra implies that identification of just one or two modes in the rings of Uranus or Neptune would eliminate a variety of interior models, and thus aid in the interpretation of Voyager observations and future spacecraft measurements.