Presentation #401.05 in the session Dynamics, Obliquities, and Tides.
Spin variations of planets determine day-night cycles and seasonal variations, playing a crucial role in planetary habitability. In compact systems, particularly in proximity to the host star, strong tidal interactions with the host star and significant perturbations due to companion planets lead to chaotic variations in planetary spin-axis. This allows planets to escape tidal locking. In this study, we present the first detailed analysis of the 3D dynamics of planet spin-axis in compact systems with strong tidal interactions. We characterize the resulting statistical properties in both day-night cycles and long-term obliquity (seasonal) variations depending on different system parameters. Applying this analysis to TRAPPIST-1, we illustrate that obliquity variation due to secular spin-orbit resonances plays an important role for the habitable zone planets, and they can result in more significant day-night variations. In addition, we illustrate the dynamical effects on planet climate using 3-d global climate models.