Understanding the origin of planetary systems : studying the Kuiper Belt and the dynamics of planet formation

Abstract

This thesis presents theoretical and observational studies pertaining to the early solar system, planet formation and extrasolar planets. First, we explore the dynamics of protoplanet formation. We find that the growth of protoplanets may be dominated by the accretion of a planetesimal disk that forms from planetesimal-planetesimal collisions, rather than direct planetesimal impacts onto the protoplanet. This has far reaching implications for the formation of planets, their growth rate and dynamics. We focus on the implications for planetary spins: it can explain the prevalence of prograde spins of planets and asteroids in the solar system, which is commonly believed to be an accident. Second, we present a series of investigations of the formation of multiple systems in the Kuiper Belt. Two of our studies are concerned with the formation of comparable mass binaries. We find that in a dynamically cold Kuiper Belt, binaries become bound predominantly by dynamical friction. This leads to a binary population with mostly retrograde mutual binary orbits. In a dynamically hot Kuiper Belt three-body gravitational interactions dominate the binary formation producing a roughly equal number of prograde and retrograde binaries. We propose a new formation scenario for Haumea’s collisional family. In our scenario, the family members are ejected while in orbit around Haumea rather than directly from Haumea’s surface as previously proposed. Our formation scenario offers an explanation for the observed velocity dispersion among the family members which is much smaller than Haumea’s escape velocity. It is consistent with detecting just one collisional family in the Kuiper Belt and aids with explaining Haumea’s initial giant impact. We conclude with observational work that aims to detect sub-km sized Kuiper Belt objects and to measure their size-distribution. Our results provide the best constraint on the surface density of small Kuiper Belt objects to date. Our findings support the idea that small Kuiper Belt objects underwent collisional evolution that modified their size distribution. We present our first candidate occultation event and show that it is unlikely to be due to instrumental artifacts or statistical fluctuations in the data.