Date of Award
Doctor of Philosophy (PhD)
Astrophysical & Planetary Sciences
Glen R. Stewart
Larry W. Esposito
Traditional models of disks around young planets and stars make a number of simplifying assumptions. These include the use of ad hoc radial temperature profiles, or isothermal disks. Another common assumption is in regard to the treatment of the outer boundary, which is allowed to expand to infinity, or neglected completely. There has also been a lack of time-dependent viscous models that include the affects of photoevaporation and/or ongoing accretion. We alleviate many of these issues by adapting numerical methods for solving propagating phase change problems to astrophysical disks in a completely novel way. These models are all viscous, time-dependent models that include a self-consistent treatment of mass loss via photoevaporation at the disk outer edge. In the case of circumplanetary disks, they also include continued accretion from the solar nebula.
I present investigations of disks around young planets and stars, made using a variety of numerical models. The investigations are primarily focused on how disk structure and evolution affect the growth and migration of growing satellite and planetary embryos. Another focus is to assess what, if any, processes are responsible for angular momentum transport in circumplanetary disks. I present detailed descriptions of these models as well as the results of applying these models to both the solar nebula and to disks around giant planets, in which regular satellites formed.
Photoevaporation can substantially truncate disks and has a similar level of affect on disk evolution and morphology as variations in the viscosity parameter, α. All of the solar nebula models were truncated, yet none of them match the steep radial surface density profile inferred from the compact configuration of the giant planets in the Nice model. Furthermore, photoevaporation has the ability to remove gas and dissipate disks on very short timescales. Despite their evolving nature, we find that giant planets and satellites can form in the evolving disks produced by these models. We conclude that steady-state circumstellar disk models are lacking and the traditional way of treating the outer boundary needs to be reexamined.
With regard to circumplanetary disks, magnetorotational instability is not a viable mechanism for angular momentum transport in the detailed 1+1D model presented here. However, temperature and density dependent opacities produce non-power law radial profiles. The deviations from power-law cause there to be increases in the radial entropy gradient. This allows for the generation of baroclinic instabilities that can be sustained and amplify. These results help alleviate the long-standing problem of angular momentum transport in circumplanetary disks and differentiate between competing models of circumplanetary disk structure.
Mitchell, Tyler Robert, "Numerical Investigations of Photoevaporative Disks: Processes Relevant to Planet and Regular Satellite Formation" (2014). Astrophysical & Planetary Sciences Graduate Theses & Dissertations. 4.