Speaker: Sam Hadden (CITA)

Title: Causes and Consequences of Chaos in Planetary Systems

Abstract: Is the solar system stable? This question garnered attention from a litany of famous scientists and mathematicians since Isaac Newton but was only properly resolved a little over a decade ago with the advent of computer hardware and algorithms capable of following the dynamical evolution of the planets for billions of years. We now know that the solar system will most likely remain stable for the remainder of the Sun’s main-sequence lifetime, though there is a ~1% chance that Mercury is destabilized and collides with Venus or the Sun. The surprising fact of the solar system’s dynamically fragile state has led some to speculate that additional planets were present earlier in the system’s history, but they have since been lost to collisions or ejections as their presence resulted in a more rapidly unstable system. Shortly after our modern understanding of the solar system’s long-term stability was established, the number of known exoplanet systems grew dramatically thanks to the NASA Kepler mission. Some evidence suggests that many of these exoplanetary systems are perched on the verge of instability and long-term dynamical evolution plays an important role in shaping their orbital architectures. The potential for the solar system to exhibit instability is intimately related to the fact that it is a chaotic dynamical system and a more general understanding of chaotic behaviour in planetary systems is necessary for determining its role shaping orbital architectures. The need for theoretical advances is especially acute since direct numerical simulations, already challenging in the case of the solar system, are impractical given the large number of exoplanet systems, their uncertain masses and orbital properties, and their much older ‘dynamical’ ages. I will describe some recent results on the causes of chaos and dynamical instability in planetary systems, focussing especially on compact systems of low-mass planets like those discovered by Kepler.