Extrasolar planet surveys have identified an abundant new population of highly irradiated planets with sizes that are in between that of the Earth and Neptune. Such planets are unlike anything found in our own Solar System, and many of their basic properties are not understood. As such, these planets provide a fundamental test for models of planets formation and evolution with important implications for the formation of the Earth and planet habitability.
In order to understand these new classes of planets, we have developed planetary structure and evolution models that can be used both to answer questions about individual planetary systems and to study populations of planets as a whole. In brief, these models allow us
to follow a planet's mass, size, internal structure, and composition as it ages; from the time it finishes formation until it is detected billions of years later.
These evolution models are critical because a planet's composition can change substantially over its lifetime. Close-in planets, like most of those found so far, are bombarded by large amounts of ionizing radiation, which over time can completely strip away a planet's atmosphere; even turning a gas-rich Neptune sized planet into a barren rocky super-Earth.
Using these models, we explore the structure, composition, and evolution of sub- Neptune sized extrasolar planets found by NASA's Kepler mission. We examine the relationships between planetary masses, radii, and compositions. We show how these compositions
have been sculpted by photo-evaporation, and we examine the interplay between thermal and evaporative evolution.