Abstract

Disc Instability theory proposes that self-gravitating discs fragment into bound objects with masses around the giant planet/brown dwarf boundary, which is attractive for explaining planetary systems with large bodies at large semimajor axis. In its most recent incarnation, Tidal Downsizing, the disc fragments may obtain solid cores through sedimentation, migrate inwards and be tidally stripped, forming objects with a range of masses and properties.

I will present several investigations of disc fragmentation and tidal downsizing, which include high resolution radiation hydrodynamic simulations and state-of-the-art semi-analytic population synthesis models. The combined evidence is clear that disc fragments have a high mortality rate. The survivors (bound and free floating) are well within the means of current direct imaging surveys, as we demonstrate through synthetic observations, placing strong constraints on how frequently discs fragment.

However, even if fragments don’t survive, the fragmentation process irrevocably alters the disc chemistry. I will show preliminary work demonstrating that while disc instability might not be the principal formation mechanism for giant planets and brown dwarfs, it sets the initial dynamical and compositional conditions for planet formation by core accretion.