UC Santa Cruz

The Kepler mission has enabled a detailed investigation of the intrinsic population of exoplanets in our galaxy. In period-radius space, the distribution of these planets reveals distinct structures that offer clues to the history of planet formation and evolution. This dissertation focuses on the demographics of sub-Neptunes and explores their connections to possible evolutionary mechanisms.By measuring planet occurrence rates, we gain insights into the underlying exoplanet population. I computed occurrence rates for Kepler planets with radii between 0.5 and 16 R⊕ and orbital periods between 1 and 400 days. Particular attention is given to the largest sub-Neptunes near the radius cliff– a sharp decline in occurrence around 3 R⊕. I compare the observed distribution to theoretical models that produce the radius valley and find that these models cannot reproduce the steepness of the observed cliff, suggesting alternative formation pathways. To help distinguish between these possibilities, I examine young planetary systems. In this context, I confirm two planets orbiting a 75 Myr-old star in the Alpha Persei cluster. These planets are notable for their near mean-motion resonance and offer the potential for mass measurements through transit timing variations. Continued atmospheric characterization and future planet detection missions will be critical to unraveling the formation and evolution histories of sub-Neptunes.