S14: The Tidal Evolution of the Earth-Moon System

Mohammad Farhat,
IMCCE/Observatoire de Paris, PSL-University, Sorbonne Université, Paris, France

Web Lecture on January 19,  2023 at 3:00 PM (Paris Time)

We revisit the evolution history of the Earth-Moon distance. Available geological data provide snapshots of the lunar orbital history, the earliest registered to date at about 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 neighbour at ~4.4 Ga is yet to be established. Namely, previous models of this reconstruction are often empirical, or numerically costly, and are always incompatible with the well-constrained lunar age. We undertake here a systematic exploration of the time-varying tidal dissipation in the Earth’s oceans and solid interior to provide, for the first time, a history of the lunar orbit that fits the present measurement of its recession and the estimated lunar age. Our work extends a lineage of earlier works on the analytical treatment of fluid tides on varying bounded surfaces, further coupled with bodily solid tidal deformations. We obtain a history of the lunar orbit that is predominantly shepherded by robust resonant excitations in the Earth’s paleo-oceans. These resonances caused significant and, relatively, rapid variations in the lunar semi-major axis, the Earth’s length of the day, and the Earth’s obliquity. These astronomical features could have driven paleo-climatic variations through tidal heating and the changing insolation. Finally, by its striking agreement with the recent geological determination of the precession frequency, our solution demonstrates the robustness of the cyclostratigraphic method in unraveling astronomical quantities from sedimentary sequences.

Reference : Farhat, Mohammad; Auclair-Desrotour, Pierre; Boué, Gwenaël; Laskar, Jacques, 2022, The resonant tidal evolution of the Earth-Moon distance, Astronomy and Astrophysics, vol. 665, pp. L1, 2022, doi:10.1051/0004-6361/202243445