"Companions as Clues: Understanding Hot Jupiter Formation"

Hot Jupiters were long thought to be lonely planets. This correctly describes the majority of the population and strongly motivates high-eccentricity tidal migration as the most common method of taking a hot Jupiter to its final short-period orbit. However, a growing number of systems now reveal nearby planetary companions. In this talk, I will discuss recent theoretical and observational results exploring the origin and evolution of hot Jupiters, with a particular focus on those with adjacent companion planets. I show that high-eccentricity tidal migration is generally incompatible with the survival of close-in companions except in very particular scenarios. I further demonstrate that while inner companions are dynamically robust, outer companions can be driven out of the transiting plane through secular interactions, stellar evolution, and stellar obliquity, potentially explaining their apparent absence in some systems. With this in mind, I present the discovery and characterization of the TOI-4468 system as a case study, highlighting how its unique architecture (an outer companion planet, but no inner companion) constrains its dynamical history. The full observational evidence suggests that while most isolated hot Jupiters likely formed through tidal migration, systems with nearby companions preferentially assembled in dynamically cold, disk-mediated ways, revealing multiple formation pathways for close-in giant planets.