Accepted manuscript JGR-Planets Tidal Evolution of the Evection Resonance/Quasi-Resonance and the Angular Momentum of the Earth-Moon System R. Rufu and R. M. Canup Planetary Science Directorate, Southwest Research Institute, Boulder, Colorado, 80302, USA Key Points: • Evection resonance and a subsequent quasi-resonance regime may remove an- gular momentum from the Earth-Moon system. • Only a narrow range of fixed tidal parameters can reconcile a high-angular momentum Moon-forming impact with the current Earth-Moon system. • For a time-dependent terrestrial dissipation model, quasi-resonance escape oc- curs early, leaving the system with an angular momentum excess. arXiv:2008.02968v1 [astro-ph.EP] 7 Aug 2020 Corresponding author: R. Rufu,
[email protected] –1– Accepted manuscript JGR-Planets Abstract Forming the Moon by a high-angular momentum impact may explain the Earth- Moon isotopic similarities, however, the post-impact angular momentum needs to be reduced by a factor of 2 or more to the current value (1 LEM) after the Moon forms. Capture into the evection resonance, occurring when the lunar perigee precession pe- riod equals one year, could remove the angular momentum excess. However the ap- propriate angular momentum removal appears sensitive to the tidal model and chosen tidal parameters. In this work, we use a constant-time delay tidal model to explore the Moon’s orbital evolution through evection. We find that exit from formal evec- tion occurs early and that subsequently, the Moon enters a quasi-resonance regime, in which evection still regulates the lunar eccentricity even though the resonance an- gle is no longer librating.