Understanding Demographics of Small Close-in Exoplanets

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Understanding Demographics of Small Close-in Exoplanets

Ho, Sze Kay Cynthia; (2025) Understanding Demographics of Small Close-in Exoplanets. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Exoplanets (planets beyond our own Solar System) offer profound insights into Earth’s origin and dynamics. Over the past years, NASA has launched dedicated missions to search for and characterise exoplanets of various sizes around different types of stars using the transit detection method. In this thesis, I perform a large-scale study of transiting small exoplanets that are close to their host stars, to better understand the formation and evolution mechanisms of planets. Using the vast amount of data collected by NASA space-based satellites such as \textit{Kepler} and \textit{TESS}, I fit planetary transits to understand the demographics of planetary sizes. I analyse the 1-minute \textit{Kepler} light curves of over 500 small (planetary radii between 1 and 4 Earth radii), close-in (orbital period between 1 and 100 days) planets, the majority of which have not been previously homogeneously analysed in this way. I update the planetary parameters, revealing a deeper radius valley for FGK host stars compared to several other investigations, suggesting that planets are likely to have more homogeneous internal compositions at formation than was previously realised. I also investigate the dependence of the radius valley with stellar mass. I observe that the radius valley becomes shallower towards lower mass stars. Upon rigorous statistical comparison, I find that theoretical planetary atmospheric mass-loss models underpredict the number of planets observed inside the radius valley for low-mass stars. I propose that this provides evidence for the presence of icy planets or collision events around low-mass stars. Finally, I present some initial results on an occurrence rate study of small, close-in planets around different stellar types. I perform systematic planet searches on \textit{TESS} light curves using the box-fitting least-squares (BLS) method, and undergo vetting processes to identify true planetary candidates. This study will shed light on the underlying mechanisms of planetary formation and evolution.

Type:	Thesis (Doctoral)
Qualification:	Ph.D
Title:	Understanding Demographics of Small Close-in Exoplanets
Open access status:	An open access version is available from UCL Discovery
Language:	English
Additional information:	Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification:	UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics UCL
URI:	https://discovery.ucl.ac.uk/id/eprint/10204482