Dynamics of Small Bodies in Planetary System Formation

Abstract

One of the most exciting astronomical developments of the past two decades has been the wealth and diversity of exoplanetary systems. Among the more exotic discoveries is a collection of planets in tight binary star systems. The first three chapters of this thesis focus on planet formation around binary stars. We assume that cores of giant planets form via collisional agglomeration of small planetesimals. A simple-minded estimate suggests that collision velocities between kilometer-sized planetesimals in some planet-hosting binary systems would be too large by a factor of $\sim 1000$ for them to grow in mutual collisions rather than being destroyed. To study this issue in more detail, we developed a model for the dynamics of planetesimals in binary systems. Chapter 1 discusses the gravitational effects of the disk on the planetesimals, and derives an expression for the disturbing function of an eccentric disk. Chapter 2 applies the results of chapter 1, as well as some additional work done by Roman Rafikov and myself incorporating the effect of gas drag from the disk, to the particular case of circumbinary planets. Chapter 3 describes our ongoing efforts to simulate the coagulation process, using the rates and collisional outcomes calculated in our other works.

Chapters 4 and 5 address the topic of small bodies in our own solar system. Recent wide-field surveys have discovered a few thousand minor solar-system bodies at tens of AU from the Sun. Upcoming surveys such as LSST should find at least an order of magnitude more. Chapter 4 describes simulations of long-period comet orbits, and predicts the orbital element distribution of the long-period comet population with perihelion between 5 and 45 AU. Chapter 5 investigates what happens if there are several Mars--Earth mass bodies left over after the giant planets are assembled. We find that their influence naturally creates a detached disk (a set of moderately inclined objects with perihelia well beyond the orbit of Neptune, but aphelia inside 1,000 AU), and also suggest the possibility that there could be an undetected Mars--Earth sized planet a few hundred AU from the Sun.