Planets Through Time: Understanding the Evolution and Diversity of Planetary Systems

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With over 4000 exoplanets discovered to date, and many more expected in the coming years, we are living through a golden age of exoplanet discovery. We now know that planetary systems exhibit a wide diversity in their properties, and that our own Solar System is not typical. For example, we have found planets like Jupiter on orbits of only a few days (so called "hot Jupiters"), planetary systems containing multiple small planets on tightly packed orbits that are all smaller than Mercury's and, perhaps most surprising of all, we have discovered that planets with sizes between those of the Earth and Neptune are the most common, yet we have no such analogues in our own Solar System. The processes that govern how planetary systems develop into the diverse population that we observe are thought to occur during the first billion years after their formation. As known exoplanets typically orbit old stars like our Sun, which are more than a billion years old, it is difficult to unravel the processes that drove their early evolution as these processes have already finished. To understand the early evolution of planetary systems, we need to detect young planets, which are still in the processes of evolving; this is the aim of our programme. Transiting planets, whose orbital plane aligns with Earth so that they periodically pass in front of (i.e. transit) their host star, are the most valuable as they can be studied in greatest detail. We will search for young transiting planets in the combined dataset of two leading exoplanet surveys, the Next Generation Transit Survey (NGTS) and the Transiting Exoplanet Survey Satellite (TESS). The young planets that we detect will help us to understand the processes that drive the early evolution of planetary systems into the diverse population that we observe. They will also provide a link between (i) our theories of planet formation and early evolution and (ii) the known (old) exoplanet population. Furthermore, they will help us to understand some intrinsic properties of exoplanets themselves, such as why some hot Jupiters appear to be larger than we expect, and why there is a dearth of planets on short orbital periods that are just under twice the size of Earth.Finally, the majority of transiting planets detected to date are thought to have migrated from where they formed in towards their host star. Such significant migration did not occur in our Solar System. Ultimately, this work will help us to understand the observed diversity of transiting planet systems, as well as why the seemingly ubiquitous migration process did not progress in our Solar System.