In the widely accepted core accretion model of planet formation, small rocky and/or icy bodies (planetesimals) accrete to form protoplanetary cores. Gas giant planets are believed to have solid cores that must reach a critical mass, ∼10 Earth masses (ME), after which there is rapid inflow of gas from the gas disk. In order to accrete the gas giants’ massive atmospheres, this step must occur within the gas disk’s lifetime (1 − 10 million years). Numerical simulations of solid body accretion in the outer Solar System are performed using two integrators. The goal of these simulations is to investigate the effects of important dynamical processes instead of specifically recreating the formation of the Solar System’s giant planets. The first integrator uses the Symplectic Massive Body Algorithm (SyMBA) with a modification to allow for planetesimal fragmentation. Due to computational constraints, this code has some physical limitations, specifically that the planetesimals themselves cannot grow, so protoplanets must be seeded in the simulations. The second integrator, the Lagrangian Integrator for Planetary Accretion and Dynamics (LIPAD), is more computationally expensive. However, its treatment of planetesimals allows for growth of potential giant planetary cores from a disk consisting only of planetesimals. Thus, this thesis’ preliminary simulations use the first integrator to explore a wider range of parameters while the main simulations use LIPAD to further investigate some specific processes. These simulations are the first use of LIPAD to study giant planet formation and they identify a few important dynamical processes affecting core formation. Without any fragmentation, cores tend to grow to ∼2ME. When planetesimal fragmentation is included, the resulting fragments are easier to accrete and larger cores are formed (∼4ME). But, in half of the runs, the fragments force the entire system to migrate towards the Sun. In other half, outward migration via scattering off a large number of planetesimal helps the protoplanets grow and survive. However, in a preliminary set of simulations including protoplanetary fragmentation, very few collisions are found to result in accretion so it is difficult for any cores to form. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-08-20 14:48:39.443

This thesis describes efforts to improve the realism of numerical models of giant planet formation and migration in an attempt to better understand these processes. A new approach has been taken to the modelling of accretion, designed to mimic reality by allowing gas to accumulate upon a protoplanetary surface. Implementing this treatment in three-dimensional self-gravity radiation hydrodynamics calculations provides an excellent model for planet growth, allowing an exploration of the factors that affect accretion. Moreover, these calculations have also been extended to investigate the migration of protoplanets through their parent discs as they grow. When focusing on the growth of non-migrating protoplanets, the models are performed using small sections of disc, enabling excellent resolution right down to the core; gas structures and flow can be resolved on scales from ~ 10^4 to 10^11 metres. Using radiative transfer, these models reveal the importance of opacity in determining the accretion rates. For the low mass protoplanets, equivalent in mass to a giant planet core (~ 10 M⊕), the accretion rates were found to increase by up to an order of magnitude for a factor of 100 reduction in the grain opacity of the parent circumstellar disc. However, even these low opacities lead to growth rates that are an order of magnitude slower than those obtained in locally-isothermal conditions. For high mass protoplanets (>~ 100M⊕), the accretion rates show very little dependence upon opacity. Nevertheless, the rates obtained using radiative transfer are still lower than those obtained in locally-isothermal models by a factor of ~2, due to the release of accretion energy as heat. Only high mass protoplanets are found to be capable of developing circumplanetary discs, and this ability is dependent upon the opacity, as are the scaleheights of such discs. However, their radial extents were found to be independent of the opacity and the protoplanet mass, all reaching ≈ RH/3, inline with analytic predictions. Migration is investigated using global models, ensuring a self-consistently evolved disc. Using locally-isothermal calculations, it was found that the capture radius of an accreting sink particle, used to model a protoplanet without a surface, must be small (<< RH) to yield migration timescales consistent with linear theory of Type I migration. In the low mass regime of Type I migration, accreting sinks with such small radii yield timescales consistent with those models in which a protoplanetary surface is used. However, for high mass protoplanets, undergoing Type II migration, the surface treatment leads to faster rates of migration, indicating the importance of a realistic accretion model. Using radiative transfer, with high opacities, leads to a factor of ~ 3 increase in the migration timescale of the lowest mass protoplanets, improving their chances of survival. As suitable gas giant progenitors, their survival is key to understanding the growth of giant planets. An unexpected result of the radiative transfer was a reduction in the migration timescale of high mass planets. This appears to be a result of the less thoroughly evacuated gaps created by planets in non-locally-isothermal discs, which affects the corotation torque.