The diversity of exoplanet systems

The possibility of planets orbiting other stars has been a topic of fascination for centuries. We are the first generation that has brought these planets - now known as exoplanets - from the realm of science-fiction into that of science. An important milestone was the discovery of several planets orbiting a pulsar (Wolszczan & Frail, 1992), followed by the first planet orbiting a star more similar to our Sun (Mayor & Queloz, 1995), an achievement recently awarded the Nobel Prize in Physics. The 25 years since have been filled with an abundance of exciting discoveries and today we know over 4000 exoplanets. These planets exhibit an incredible diversity of properties. Why do so many planets have tiny orbits - often much smaller than that of Mercury? What causes planets to become rocky, gaseous, or something in between? Why do some planets have orbits that are strongly eccentric, or misaligned with the rotation of their host stars? What happens to planets when stars evolve away from the main sequence? Which planets are the most favourable and interesting targets for studies of their atmospheres? How unique is our solar system - are we alone?

Despite the discovery of thousands of new planets over the last years, much remains unknown about their characteristics. A powerful way of learning about exoplanets is by combining information from different detection methods, in particular from transit surveys such as the NASA Kepler and TESS missions, and from radial velocity (RV) observations from state-of-the-art instruments on telescopes around the world such as the ESO Very Large Telescope in Chile. By combining these sources of data, both sizes and masses of planets can be measured and their composition can be inferred. In this way, we can classify the architecture and diversity of planetary systems. A motivated PhD student will join an international team of experts focused on conducting and analysing RV observations of newly discovered transiting exoplanets. The project holds tremendous potential for a range of exciting new discoveries. We will seek to establish which planets have thick atmospheres and which have no atmospheres, and investigate the reasons for these differences. The student will tap into a large international network of experts to do this challenging but exciting work.