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Constraining Saturn’s Interior with Ring Seismology: Effects of Differential Rotation and Stable Stratification

Dewberry, Janosz W. and Mankovich, Christopher R. and Fuller, Jim and Lai, Dong and Xu, Wenrui (2021) Constraining Saturn’s Interior with Ring Seismology: Effects of Differential Rotation and Stable Stratification. Planetary Science Journal, 2 (5). Art. No. 198. ISSN 2632-3338. doi:10.3847/PSJ/ac0e2a.

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Normal mode oscillations in Saturn excite density and bending waves in the C ring, providing a valuable window into the planet's interior. Saturn's fundamental modes (f-modes) excite the majority of the observed waves, while gravito-inertial modes (rotationally modified g-modes) associated with stable stratification in the deep interior provide a compelling explanation for additional density waves with low azimuthal wavenumbers m. However, multiplets of density waves with nearly degenerate frequencies, including an m = 3 triplet, still lack a definitive explanation. We investigate the effects of rapid and differential rotation on Saturn's oscillations, calculating normal modes for independently constrained interior models. We use a non-perturbative treatment of rotation that captures the full effects of the Coriolis and centrifugal forces, and consequently the mixing of sectoral f-modes with g-modes characterized by very different spherical harmonic degrees. Realistic profiles for differential rotation associated with Saturn's zonal winds can enhance these mode interactions, producing detectable oscillations with frequencies separated by less than 1%. Our calculations demonstrate that a three-mode interaction involving an f-mode and two g-modes can feasibly explain the finely split m = 3 triplet, although the fine-tuning required to produce such an interaction generally worsens agreement with seismological constraints provided by m = 2 density waves. Our calculations additionally demonstrate that sectoral f-mode frequencies are measurably sensitive to differential rotation in Saturn's convective envelope. Finally, we find that including realistic equatorial antisymmetry in Saturn's differential rotation profile couples modes with even and odd equatorial parity, producing oscillations that could in principle excite both density and bending waves simultaneously.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Dewberry, Janosz W.0000-0001-9420-5194
Mankovich, Christopher R.0000-0002-4940-9929
Fuller, Jim0000-0002-4544-0750
Lai, Dong0000-0002-1934-6250
Xu, Wenrui0000-0002-9408-2857
Additional Information:© 2021. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 April 20; revised 2021 June 20; accepted 2021 June 22; published 2021 September 21. The authors thank the two anonymous referees who reviewed this work, both of whom provided very thorough and constructive comments that significantly improved the quality of the paper. J.W.D. is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), funding reference No. CITA 490888-16.
Group:TAPIR, Walter Burke Institute for Theoretical Physics, Astronomy Department
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)CITA 490888-16
Subject Keywords:Planetary science; Planetary structure; Solar system; Saturn; Hydrodynamics; Pulsation modes
Issue or Number:5
Classification Code:Unified Astronomy Thesaurus concepts: Planetary science (1255); Planetary structure (1256); Solar system (1528); Saturn (1426); Hydrodynamics (1963); Pulsation modes (1309)
Record Number:CaltechAUTHORS:20211012-211828363
Persistent URL:
Official Citation:Janosz W. Dewberry et al 2021 Planet. Sci. J. 2 198
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111382
Deposited By: George Porter
Deposited On:13 Oct 2021 14:57
Last Modified:13 Oct 2021 14:57

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