Princeton University Extrasolar Planet Discussion Group

Despite the thousands of planets discovered orbiting stars on the main sequence, the planetary systems of more evolved stars remain poorly understood. Studying planetary systems around subgiant and red giant stars can reveal how planetary systems respond to stellar evolution at the end of their life cycle. Over the last 5 years, the 'Giants Transiting Giants' survey has increased the number of planets known to be transiting evolved stars by a factor of three. These planetary systems provide testbeds for understanding planet inflation, orbital alignment, decay, and chaotic disruption, planet engulfment and related chemical enhancement of host stars. Recent studies have revealed that the orbital configurations of these systems differ from those of main sequence systems--planets around evolved stars seem to follow unique period-eccentricity and orbital alignment trends that are not seen in main sequence systems. Furthermore, the discovery of a low-density hot Neptune around a red giant star suggests that these planets are more resilient to atmospheric erosion than previously thought. Currently proposed studies of these and similar systems with JWST and new ground-based facilities will reveal how planet atmospheres respond to the evolution of their host stars in the next few years, and future missions like Roman will identify thousands of these systems and revolutionize evolved system demographics in the upcoming decade.