| dc.description.abstract | Protoplanetary discs can be dynamically unstable due to structure induced
by an embedded giant planet. In this thesis, I discuss the stability of such
systems and explore the consequence of instability on planetary migration.
I present semi-analytical models to understand the formation of the unstable
structure induced by a Saturn mass planet, which leads to vortex formation.
I then investigate the effect of such vortices on the migration of a Saturnmass
planet using hydrodynamic simulations. I explain the resulting nonmonotonic
behaviour in the framework of type III planetary migration.
I then examine the role of disc self-gravity on the vortex instabilities. It
can be shown that self-gravity has a stabilising effect. Linear numerical
calculations confirms this. When applied to disc-planet systems, modes
with small azimuthal wavelengths are preferred with increasing disc selfgravity.
This is in agreement the observation that more vortices develop in
simulations with increasing disc mass. Vortices in more massive discs also
resist merging. I show that this is because inclusion of self-gravity sets a
minimal vortex separation preventing their coalescence, which would readily
occur without self-gravity.
I show that in sufficiently massive discs vortex modes are suppressed. Instead,
global spiral instabilities develop. They are interpreted as disturbances
associated with the planet-induced structure, which interacts with
the wider disc leading to instability. I carry out linear calculations to confirm
this physical picture. Results from nonlinear hydrodynamic simulations
are also in agreement with linear theory. I give examples of the effect of
these global modes on planetary migration, which can be outwards, contrasting
to standard inwards migration in more typical disc models.
I also present the first three-dimensional computer simulations examining
planetary gap stability. I confirm that the results discussed above, obtained
from two-dimensional disc approximations, persist in three-dimensional discs. | |
