The properties of transiting exoplanets

  • Robert Wells

Student thesis: Doctoral ThesisDoctor of Philosophy


This thesis focuses on transit events; both the detectability of the Solar system planets and the detection of extra-solar planets. I start by flipping the concept of exoplanet transit events and stated where transits of the Solar system planets could be observed from. We call these regions of visibility “transit zones” which trace the shadows of the planets outwards from the Sun. I estimated the number of potentially habitable exoplanets within the Earth’s transit zone, finding that approximately ten would be currently detectable.

I then carried out a transit search for these planets, plus other interesting systems, using data from the Kepler-K2 mission which uniquely pointed at fields along the ecliptic plane. This led to my discovery of three super-Earths and one planet candidate orbiting the M1 dwarf K2-133. I later conducted a follow-up study on the K2-133 system, where I further constrained the stellar and planetary properties using the Gaia DR2 parallax distance, and WHT/LIRIS NIR spectra. I also statistically validated the planet candidate (planet e) – a fourth super-Earth in the system. This new planet orbits on the edge of the star’s temperate zone and prompts discussion on its potential composition and habitability.

The final pieces of work of the thesis focus more on radial velocities, rather than transit events. From a transit search of K2 M-dwarfs, I compiled a list of so-called “monster” planet candidates – Jupiter-sized planets orbiting M-dwarfs. I plan obtain high-resolution spectra of these targets in order to measure changes in the stellar radial velocity to infer masses of the transiting bodies, to confirm or rule out their planetary nature. Such planets are a current challenge to the core accretion planet formation theory, and therefore, a significant population of these worlds would support gravitational instability being a more dominant formation process. Finally, I linked TESS targets of interest to catalogues of archival radial velocity spectra. Many bright stars have been monitored by radial velocity surveys without detecting planets around them. However, if a planet’s transit is detected by TESS, the degeneracy of radial velocity parameters can be broken. This has been successful in the discovery of two planetary systems so far, demonstrating its effectiveness.
Date of AwardJul 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SponsorsNorthern Ireland Department for the Economy
SupervisorChristopher Watson (Supervisor) & Neale Gibson (Supervisor)


  • exoplanets
  • exoplanet transits
  • planet formation
  • low-mass stars
  • Kepler-K2
  • M-dwarfs

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