Tidal evolution and detectability of close-in star-planet and planet-moon systems

The properties of close in giant planets challenge the current models of planetary formation and evolution. Since any pair of extended bodies in proximity will strongly interact and exchange angular momentum with each other—deforming their shape due to gradients in their gravitational field—these systems can help us test tidal models and work as a probe to constrain the interior structure of stars and planets. Considering the systematic discovery of giant exoplanets with orbits of a few days (or less than a day in some cases) over the last four decades, in this thesis I investigate how stellar gravitational forces through tidal interactions affect the evolution of short-period and ultra-short-period Jupiters (USP-Js) orbiting younger and older stars. I developed comprehensive models that include effects such as photo-evaporation of the planet’s atmosphere, stellar wind, stellar spin-up, and loss of material from the star and the planet. I study the tidal evolution of the aforementioned systems by exploring the dissipation of energy via inertial waves in stellar/planetary convective envelopes, viscoelastic energy dissipation in planetary solid cores, as well as internal gravity waves in stellar radiative regions.

In the most extreme cases, tidal interactions will make close-in giant planets undergo orbital decay that could eventually lead to their destruction within the Roche limit. Despite the systematic prediction of orbital decay by tidal models, no observational evidence has yet been found. I demonstrate that the rate of orbital decay of some USP-Js studied in this thesis is so rapid that measurements of their decay (by detecting shifts in their mid-transit times) could be made within the next few years. Furthermore, since tidal interactions can also affect any nearby companion orbiting close-in giant planets, I also delve into how potential moons orbiting these exoplanets—‘exomoons’—will be tidally perturbed, as well as the possibility of ring systems forming around these planets or moons.

Finally, I investigate how some of the features of close-in giant planets (e.g. their rings) can be used to develop new robust techniques that would complement the search for exoplanetary systems. Since transits and radial velocity measurements (RVs) are biased towards Jupiter-like planets in close-in orbits, I show how light that is reflected from planetary rings can be used to discover new giant planets with orbital architectures where transits and RVs are deemed inefficient. Overall, the body of work presented in this thesis contributes new insights to our understanding of close-in planetary systems, the role of tidal interactions on their evolution, as well as their detectability.