Anders Johansen
Professor
Formation and Early Evolution of Planetary Systems
Author
Summary, in English
Over the past 20 years we have discovered that exoplanets are common in the Galaxy, and are far more diverse than anyone expected. Half of all Sun-like stars are accompanied by at least one super-Earth (a planet with a size between Earth and Neptune), many planets have very high eccentricities indicative of a dynamical origin, and a small fraction of stars are accompanied by hot Jupiters, whose origin is poorly understood. In this thesis I investigate the formation and dynamical evolution of planetary systems. In half of this thesis I develop constraints for the formation of planetesimals by the runaway convergence of radial migration known as the streaming instability, and apply the result to a computer model of a photo-evaporating protoplanetary disk. In the rest of this thesis I study the dynamical stability of planetary systems with multiple giant planets in order to learn about the past history of exoplanet systems.
All of my work relies heavily on computer modelling. I used hydrodynamic simulations of a shearing box inside a protoplanetary disk to determine the dust-to-gas ratio needed to trigger the streaming instability as a function of particle size. Similarly, the protoplanetary disk model is a one-dimensional hydrodynamic model that includes sink terms for photoevaporative outflows. The dynamical evolution of planetary systems occurs after planet formation is complete and the disk has fully dissipated. Dynamical simulations were performed with an N-body code designed for long-term modelling of planetary orbits.
My work has shown that the streaming instability is active for smaller particles than previously thought possible. I also found that in a protoplanetary disk, planetesimals begin to form early in the outer disk, where photoevaporation can more easily remove the gas component. As the disk evolves, planetesimal formation moves inward. From my dynamical simulations I am able to use present-day observations to estimate the probability that a habitable planet would have survived in a given planetary system, and I can estimate the masses of the planets that suffered ejections or collisions in that system.
All of my work relies heavily on computer modelling. I used hydrodynamic simulations of a shearing box inside a protoplanetary disk to determine the dust-to-gas ratio needed to trigger the streaming instability as a function of particle size. Similarly, the protoplanetary disk model is a one-dimensional hydrodynamic model that includes sink terms for photoevaporative outflows. The dynamical evolution of planetary systems occurs after planet formation is complete and the disk has fully dissipated. Dynamical simulations were performed with an N-body code designed for long-term modelling of planetary orbits.
My work has shown that the streaming instability is active for smaller particles than previously thought possible. I also found that in a protoplanetary disk, planetesimals begin to form early in the outer disk, where photoevaporation can more easily remove the gas component. As the disk evolves, planetesimal formation moves inward. From my dynamical simulations I am able to use present-day observations to estimate the probability that a habitable planet would have survived in a given planetary system, and I can estimate the masses of the planets that suffered ejections or collisions in that system.
Department/s
- Lund Observatory - Has been reorganised
Publishing year
2016-10
Language
English
Document type
Dissertation
Publisher
Lund University, Faculty of Science, Department of Astronomy and Theoretical Physics
Topic
- Astronomy, Astrophysics and Cosmology
Keywords
- planet formation
- planets and satellites: dynamical evolution and stability -- planets and satellites: gaseous planets -- planets and satellites: terrestrial planets
- planets and satellites: terrestrial planets
Status
Published
Project
- Formation and Early Evolution of Planetary Systems
- From pebbles to planets: towards new horizons in the formation of planets
Supervisor
- Anders Johansen
- Melvyn B Davies
ISBN/ISSN/Other
- ISBN: 978-91-7623-979-7
- ISBN: 978-91-7623-978-0
Defence date
24 November 2016
Defence time
09:00
Defence place
Lund Observatory, Lundmark lecture hall, Sölvegatan 27, Lund
Opponent
- Sean Raymond (Dr.)