Evolution models of TOI-270d. Top panel : planetary radius as a function of age. The black errorbar corresponds to the measured radius and age. Since the age is uncertain, we adopted an age range of 1 to 10 Gyr. Bottom panel: heavy-element mass fraction at the end of the evolution as a function of pressure. The orange and blue shaded areas show the observed atmospheric metal and water mass fractions, respectively (from Benneke et al. 2024).