Séminaire / Seminar GReCO |
| « On planetary fluid tides: the sixty-year-old “time-scale problem” of the Lunar origin » |
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Mohammad Farhat |
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The Sun, Earth, and Moon trio dances to rhythms of mutual gravitational tidal interactions. Consequently, ever since the Moon formed close to the Earth, it has been forced to drift away through orbital angular momentum pumping. Available geological data on Earth provide snapshots of the lunar orbital history, the earliest registered to date at ~3.2 Ga. However, a complete theoretical reconstruction of the lunar orbit, which traces its evolution from the present state to a post-impact nosy neighbor at ~4.5 Ga is yet to be established. Namely, previous models of this reconstruction are either empirical, or numerically costly, and are always incompatible with the estimated lunar age. In this talk, I present our exploration of the time-varying tidal dissipation in the Earth's paleo-oceans to provide, for the first time, a history of the lunar orbit that fits the present measurement of its recession, the lunar age, and the available geological proxies. This work extends a lineage of earlier ones on the analytical treatment of fluid tides over varying bounded surfaces, further coupled with solid bodily tidal deformations. The resulting evolution of the Earth-Moon history involves multiple crossings of prominent resonances in the tidal dissipation that caused significant and, relatively, abrupt variations in the lunar orbital distance, the Earth’s length of the day, obliquity, and precessional motion. Consequently, these astronomical features should have driven major paleo-climatic variations through the changing insolation. Coupling between oceanic and solid planetary tides, our effective tidal model requires a reduced number of free parameters, thus allowing its utilization outside our home. An eminently classical dynamical tale revived for the exoplanetary 21st century!
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lundi 25 mars 2024 - 11:00 Salle des séminaires Évry Schatzman Institut d'Astrophysique de Paris |
| Pages web du séminaire / Seminar's webpage |