Resonant Stratification in Titan’s Global Ocean
Titan’s ice shell floats on top of a global ocean, as revealed by the large tidal Love number k _2 = 0.616 ± 0.067 registered by Cassini. The Cassini observation exceeds the predicted k _2 by one order of magnitude in the absence of an ocean, and is 3 σ away from the predicted k _2 if the ocean is p...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2024-01-01
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| Series: | The Planetary Science Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/PSJ/ad11ef |
| _version_ | 1797351301938413568 |
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| author | Benjamin Idini Francis Nimmo |
| author_facet | Benjamin Idini Francis Nimmo |
| author_sort | Benjamin Idini |
| collection | DOAJ |
| description | Titan’s ice shell floats on top of a global ocean, as revealed by the large tidal Love number k _2 = 0.616 ± 0.067 registered by Cassini. The Cassini observation exceeds the predicted k _2 by one order of magnitude in the absence of an ocean, and is 3 σ away from the predicted k _2 if the ocean is pure water resting on top of a rigid ocean floor. Previous studies demonstrate that an ocean heavily enriched in salts (salinity S ≳ 200 g kg ^−1 ) can explain the 3 σ signal in k _2 . Here we revisit previous interpretations of Titan’s large k _2 using simple physical arguments and propose a new interpretation based on the dynamic tidal response of a stably stratified ocean in resonance with eccentricity tides raised by Saturn. Our models include inertial effects from a full consideration of the Coriolis force and the radial stratification of the ocean, typically neglected or approximated elsewhere. The stratification of the ocean emerges from a salinity profile where the salt concentration linearly increases with depth. We find multiple salinity profiles that lead to the k _2 required by Cassini. In contrast with previous interpretations that neglect stratification, resonant stratification reduces the bulk salinity required by observations by an order of magnitude, reaching a salinity for Titan’s ocean that is compatible with that of Earth’s oceans and close to Enceladus’ plumes. Consequently, no special process is required to enrich Titan’s ocean to a high salinity as previously suggested. |
| first_indexed | 2024-03-08T12:58:17Z |
| format | Article |
| id | doaj.art-886bdf30f86449d695dd1f74fe25afd0 |
| institution | Directory Open Access Journal |
| issn | 2632-3338 |
| language | English |
| last_indexed | 2024-03-08T12:58:17Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Planetary Science Journal |
| spelling | doaj.art-886bdf30f86449d695dd1f74fe25afd02024-01-19T14:57:55ZengIOP PublishingThe Planetary Science Journal2632-33382024-01-01511510.3847/PSJ/ad11efResonant Stratification in Titan’s Global OceanBenjamin Idini0https://orcid.org/0000-0002-2697-3893Francis Nimmo1https://orcid.org/0000-0003-3573-5915Department of Earth and Planetary Sciences, University of California Santa Cruz , 1156 High Street, Santa Cruz, CA 95064, USA ; bidini@ucsc.eduDepartment of Earth and Planetary Sciences, University of California Santa Cruz , 1156 High Street, Santa Cruz, CA 95064, USA ; bidini@ucsc.eduTitan’s ice shell floats on top of a global ocean, as revealed by the large tidal Love number k _2 = 0.616 ± 0.067 registered by Cassini. The Cassini observation exceeds the predicted k _2 by one order of magnitude in the absence of an ocean, and is 3 σ away from the predicted k _2 if the ocean is pure water resting on top of a rigid ocean floor. Previous studies demonstrate that an ocean heavily enriched in salts (salinity S ≳ 200 g kg ^−1 ) can explain the 3 σ signal in k _2 . Here we revisit previous interpretations of Titan’s large k _2 using simple physical arguments and propose a new interpretation based on the dynamic tidal response of a stably stratified ocean in resonance with eccentricity tides raised by Saturn. Our models include inertial effects from a full consideration of the Coriolis force and the radial stratification of the ocean, typically neglected or approximated elsewhere. The stratification of the ocean emerges from a salinity profile where the salt concentration linearly increases with depth. We find multiple salinity profiles that lead to the k _2 required by Cassini. In contrast with previous interpretations that neglect stratification, resonant stratification reduces the bulk salinity required by observations by an order of magnitude, reaching a salinity for Titan’s ocean that is compatible with that of Earth’s oceans and close to Enceladus’ plumes. Consequently, no special process is required to enrich Titan’s ocean to a high salinity as previously suggested.https://doi.org/10.3847/PSJ/ad11efTitanSaturnian satellitesOcean tidesGravitational fieldsPlanetary interiorAstrophysical fluid dynamics |
| spellingShingle | Benjamin Idini Francis Nimmo Resonant Stratification in Titan’s Global Ocean The Planetary Science Journal Titan Saturnian satellites Ocean tides Gravitational fields Planetary interior Astrophysical fluid dynamics |
| title | Resonant Stratification in Titan’s Global Ocean |
| title_full | Resonant Stratification in Titan’s Global Ocean |
| title_fullStr | Resonant Stratification in Titan’s Global Ocean |
| title_full_unstemmed | Resonant Stratification in Titan’s Global Ocean |
| title_short | Resonant Stratification in Titan’s Global Ocean |
| title_sort | resonant stratification in titan s global ocean |
| topic | Titan Saturnian satellites Ocean tides Gravitational fields Planetary interior Astrophysical fluid dynamics |
| url | https://doi.org/10.3847/PSJ/ad11ef |
| work_keys_str_mv | AT benjaminidini resonantstratificationintitansglobalocean AT francisnimmo resonantstratificationintitansglobalocean |