Extrasolar Planets

Over 5000 extrasolar planets have been discovered to date, and it is predicted that most stars in the universe are hosts to planetary systems. The diversity of the already-observed exoplanetary population hints at varying formation mechanisms. The first of the two best-studied mechanisms is core-accretion, which depends on heavy elements in the protoplanetary disc (a disc of gas and dust surrounding a young star, and the birthplace of planets) to settle into the midplane of the disc and begin to form solid cores through collisions with other solids. These cores may then pack on mass and grow into planets, of both the terrestrial and gas giant kind. However, core accretion slows down in the outer regions of the disc, where interactions between solids are less frequent. However, there exists a small but notable observed population of wide orbit gas giant planets. Therefore, a second scenario was proposed to quickly form this planet demographic through the gravitational collapse of gas in the outer region of the disc. Such a collapse into clumps of matter which will eventually form planets is called "fragmentation", and is a common process in all astrophysical discs. Fragmentation is efficient at forming giant planets quickly.

However, the paucity of wide orbit giant planets is surprising since simulations of fragmenting discs form them quite easily. It must therefore be the case that fragmentation in realistic planet-forming environments differs from the idealised scenario used in current simulations. To fill this gap, we propose a population study of a set of "realistic" protoplanetary disc simulations to understand how likely fragmentation is when the initial conditions are informed by the local environment. To this end, we extract protoplanetary discs formed around protostars in a large simulation of a collapsing gas cloud, and use these discs as initial conditions for our population study. This study will be the first of its kind, and will provide the protoplanetary disc community with valuable and much-desired information about the initial conditions of discs in realistic environments, as well as benefitting our own study of fragmentation. The study will also produce an open-source standalone tool which will be able to increase the resolution of hydrodynamical simulations, providing further benefit to the community. Finally, the methods employed in our study will allow for numerous follow-up studies looking at dynamical events which discs may encounter, understanding why disc mass distribution in simulations does not agree with observation, and studying the thermal evolution of protoplanetary clumps.