On the Spin-axis Dynamics of Planets
Gongjie Li

The variation of a planet's obliquity plays an important role in determining its climate, and the existence of massive satellites can influence such variations. For instance, the Earth's obliquity is stabilized by the Moon, and would undergo chaotic variations without the Moon. To quantify this, I will present a simplified perturbative approach I developed, and demonstrate that without the Moon, the stochastic change in the Earth's obliquity is sufficiently slow to not reach high values (>40 degrees) in billion-year timescales. In addition, I will apply this analytical approach and show that Earth obtained its current obliquity during the formation of the Moon, when the Solar System was more compact according to the Nice Model. In the end, applying similar techniques to exoplanetary systems, I will illustrate that compact planetary systems generally do not lead to larger obliquity variations.