Formation and Dynamical Evolution of Planetary Systems

Astronomy Unit School of Physics and Astronomy Queen Mary University of London Formation and Dynamical Evolution of Planetary Systems Sanson Tsun Sum Poon Supervised by Richard P. Nelson Submitted in partial fulfilment of the requirements of the Degree of Doctor of Philosophy 1 Declaration I, Sanson T. S. Poon, confirm that the research included within this thesis is my own work or that where it has been carried out in collaboration with, or supported by others, that this is duly acknowledged below and my contribution indicated. Pre- viously published material is also acknowledged below. I attest that I have exercised reasonable care to ensure that the work is original, and does not to the best of my knowledge break any UK law, infringe any third party’s copyright or other Intellectual Property Right, or contain any confidential material. I accept that the College has the right to use plagiarism detection software to check the electronic version of the thesis. I confirm that this thesis has not been previously submitted for the award of a degree by this or any other university. The copyright of this thesis rests with the author and no quotation from it or information derived from it may be published without the prior written consent of the author. Details of collaboration and publications: Sanson T. S. Poon, Richard P. Nelson, Seth A. Jacobson and Alessandro Mor- bidelli (2020). Formation of compact systems of super-Earths via dynamical instabilities and giant impacts. MNRAS 491, 5595-5620 Sanson T. S. Poon and Richard P. Nelson (2020). On the origin of the eccentricity dichotomy displayed by compact super-Earths: dynamical heating by cold giants. MNRAS 498, 5166-5182 Sanson T. S. Poon, Richard P. Nelson and Gavin A. L. Coleman (submitted). In situ formation of hot Jupiters with companion super-Earths. Signature: Sanson T. S. Poon Date: February 19, 2021 2 In memory of Chan Lin 3 Abstract Our understanding of extrasolar planetary systems has undergone a revolution in recent years due to major advances in the observations of exoplanets. Planetary system architectures are found to be very diverse, consisting of closely orbiting compact multiple systems of super-Earths and terrestrial planets, widely spaced systems of giant planets, and bodies on temperate orbits at intermediate distances from their host stars. A major unsolved question is how did these planetary systems form and evolve to create the diversity that we now observe? The focus of this thesis is to address this question using N-body simulations of planetary systems, combined with models for realistic planet-planet collisions and the nascent protoplanetary disc with prescriptions for disc-planet interactions. The aim is to adopt initial conditions similar to those thought to exist around young stars that are in the process of forming, and to construct a synthetic population of exoplanet systems for comparison with the observations, in order to test our current theories of planetary system formation. Different planetary system formation and evolution scenarios are examined in this thesis, including in situ formation and self-scattering between growing protoplanets, dynamical heating of inner planetary systems by cold gas giants, and the in situ formation of systems containing hot Jupiters and interior super-Earths. In the in situ self-scattering scenario, simulations show that the final planetary systems look broadly similar to the compact multiplanetary systems observed by Kepler. But the observed distributions of planetary multiplicities or eccentricities are not reproduced, because scattering does not excite the systems sufficiently. Post- processing the collision outcomes suggests that the planets would not significantly change the ice fractions of initially ice-rich protoplanets, but significant stripping of gaseous envelopes appears likely. Hence, it may be difficult to reconcile the observation that many low-mass Kepler planets have H/He envelopes with an in situ formation scenario that involves giant impacts after the dispersal of the gas 4 disc. In the scenario of dynamical heating of the inner planetary system by cold giants, synthetic transit observation of the final systems reveals dichotomies in both the eccentricity and multiplicity distributions that are close to being in agreement with the Kepler data. This suggested that understanding the observed orbital and physical properties of the compact systems of super-Earths discovered by Kepler may require holistic modelling that couples the dynamics of both inner and outer systems of planets during and after the epoch of formation. The in situ formation scenario demonstrates the plausibility of forming systems of a hot Jupiter with companion super-Earths, such as WASP-47, Kepler-730, and TOI-1130. Simulations show the evolution for such systems consistently follows four distinct phases: early giant impacts; runaway gas accretion onto the seed pro- toplanet; disc damping-dominated evolution of the embryos orbiting exterior to the giant; a late chaotic phase after the dispersal of the gas disc. Synthetic transit observations of the simulations provide a similar occurrence rate for systems containing a hot Jupiter and an inner super-Earth to the actual transit surveys. But simulated hot Jupiters are rarely detected as single transiting planets, in disagreement with observations. In situ formation is a viable pathway for forming systems with these unusual architectures, although not for the majority of hot Jupiters. Sanson T. S. Poon 5 Acknowledgements 雲¼¼ ++w夜á感激有z/ 雲d上滿星I 星星不知S我的/L º間{有·切的<I Ï夜往上看 — ¹VR, ÃI文 hz/i This thesis would not have been possible without the guidance and enlightenment of my supervisor, Richard Nelson. I am sincerely grateful for his time and patience throughout my time in the Astronomy Unit. I would also like to thank my second supervisor, Sijme-Jan Paardekooper, for all his support and constructive discussion. A special thanks to Jim Emerson, who provided me many helpful suggestions to choose my marvellous supervisors and research area. I have had a fantastic and enjoyable time during my Ph.D. study in the Astronomy Unit. I would like to thank everyone that I came across in the last four years, especially but not only to (in no particular order): John Ronayne and Shailee Imrith, who always are very good company in the office during all the overtimes, evenings and weekends; Maritza Soto, for all her interest- ing conversation, and our unforgettable road trip in Iceland; Pedro Carrilho and Charalambos Pittordis, for all the amazing barbecue parties; Viraj Sanghai, for all your laughs; Colin McNally, who has knowledge in almost everything both inside and outside his research area, including if Jesus wear socks in the sandals; Francesco Lovascio, for putting our photo as his online profile picture, and the enjoyable con- ference trip in Japan and Iceland; Jack Skinner, for our amusing discussions during the coffee time; Sandy Zeng, the only person that I can chat to with my native lan- guage; Domenico Trotta, for the delicious spaghetti carbonara; Jorge Venegas, for sharing my feeling when the football team that we support lost almost every week; Clark Baker, who always bring fun to everyone in the office; Louis Coates, for the free ice-skating entrance; and Christopher Gallagher, for his great sense of humour. Also, all the lecturers who gave me lectures in my Astrophysics course, including 6 Carl Murray, Guillem Anglada-Escude, James Cho, David Burgess, Will Sutherland, Sergei Vorontsov, and Alexander Polnarev; every member in the planetary group for many constructive discussions, including Craig Agnor, Nick Cooper, Richard Donnison, Edward Gillen, Thomas Haworth, Izaskun Jimenez-Serra, Gavin Cole- man, David Quenard, Ali Barlas, Kevin Chan, Paul Hallam, Matthew Mutter, John Strachan, and George Turpin, from whom I learned a lot; the cosmology group and plasma group for all the lunch-time and coffee-time chats, including Tessa Baker, Phil Bull, Bernard Carr, Christopher Chen, Chris Clarkson, Timothy Clifton, David Mulryne, Alkistis Pourtsidou, Ian Roxburgh, David Tsiklauri, Julian Adamek, Samir Choudhuri, Luca Franci, Callum Boocock, Jesse Coburn, Eline De Weerd, Jessie Durk, Alice Giroul, Fraser Kennedy, Md Goribullha Shah, Paula Soares, and spe- cially Karim Malik, our department head and the second tallest member of the Astronomy Unit; and my friendly and energetic colleagues at Royal Observatory Greenwich: Patricia Skelton, Gregory Brown, Dhara Patel, Angelos Tsiaras, Tania de Sales Marques, Anna Ross, Elizabeth Avery, Emily Drabek-Maunder, Edward Bloomer, Mikaela Webb, and Bryony Lanigan. A big and special thanks to Rebeca Martinez-Carrillo, who always supports me and makes my research time extra enjoyable. Last but not least, I am indebted to my parents and close family: Tim, San, and Amy, for all their patience and continuous support. 7 Contents Abstract4 Acknowledgements6 1. Introduction to exoplanets 12 1.1. A brief history of exoplanets....................... 12 1.1.1. From the ancient periods to the first detection......... 12 1.1.2. From the first detection to present............... 14 1.2. Detection methods............................ 15 1.2.1. Radial velocity method...................... 16 1.2.2. Transit method.......................... 20 1.2.3. Other methods.......................... 25 1.3. Exoplanets statistics........................... 30 1.3.1. Diversity of planetary systems.................. 30 1.3.2. Kepler statistics.......................... 33 1.4. Planetary system

Load more