Confirmation of Hot Jupiter Re-Inflation

Hot Jupiters are a type of gas giant exoplanet that have a mass similar to Jupiter and short (<10 days) orbital periods. Some hot Jupiters have a larger radius than is predicted by planetary evolution models and this process is aptly called planetary inflation. The causes of this phenomena have been debated for over 20 years, but in general can be classified into two mechanisms of inflation, class I and class II. Class I inflation states that as a hot Jupiter’s host star evolves, the planet can become re-inflated by the star’s increased irradiation, causing its radius to increase. Class II inflation states that the planet was already inflated during formation and continues to slowly cool as the host star’s irradiation keeps it warm. Using data from K2, Spitzer and Keck, we better constrained the mass and radius of two hot Jupiters, K2-97b and K2-132b. By measuring these two parameters, we can determine if these planets have been re-inflated by class I inflation mechanisms or simply maintained their heat from formation via class II inflation mechanisms. We find a mass and radius of these planets in strong agreement with what has been determined by previous studies, supporting evidence for planet re-inflation through class I inflation mechanisms in these systems. Furthermore, we find a marginal improvement on transit depth and planet radius constraints when including the Spitzer data in our model, placing an upper limit on the planet radii in the near infrared. Future studies of hot Jupiters transiting evolved stars may reveal the dependence of planet re-inflation on mass, composition and evolutionary state.