While the Kepler mission discovered thousands of planets around main sequence stars, red giant stars were largely unexplored. A sample of transiting planets around these more evolved stars can test theories of giant planet inflation and migration, problems that have gone unsolved for more than 20 years. Since 2016, I have led a search for transits around red giant stars with the K2 Mission to reveal the effects of stellar evolution on planet inflation, migration, and occurrence. This survey increased the number of confirmed transiting planets around red giant stars by more than 50%. Comparing these and similar planets orbiting main sequence stars to planet evolution models revealed that planets orbiting red giants may be re-inflated by the rapid evolution of their host stars. Additional followup measurements of this population showed that these planets preferentially reside on moderately eccentric orbits, suggesting that stellar evolution can also result in inward planet migration and orbit circularization. Investigating planet occurrence as a function of planet period and radius, red giant stars appear to host significantly more super-Jupiters than main sequence stars at orbital periods of 10 days or less. Together, these results provide a clearer view of how star-planet interaction drives planet evolution. Soon, the TESS Mission will shed new light on unexplored dimensions of this interaction with its predicted discovery of an order of magnitude more transiting planets orbiting evolved stars over the next two years.
