Tracing the Evolution of Short-Period Exoplanets: Insights from Young Stellar Clusters

Studying young short-period planet populations can help us better understand their primordial nature as well as how they have evolved over time. The radius valley is a feature first found in Kepler’s Gyr-old short-period planet population around Sun-like (FGK) stars. It is believed to be evolutionary in nature, likely sculpted by atmospheric mass loss – a process that can even lead to these planets losing their envelopes entirely, leaving behind just their bare cores. Theory then suggests that the primordial population of short-period sub-Neptunes could be markedly different than the Gyr-old planets observed with Kepler. Yet making such demographic comparisons requires a uniformly characterized sample of young short-period planets, which were not abundant in the Kepler field. There is thus a need for a survey focused on young stellar clusters, whose planets represent a sample much closer in time to the primordial planet population, before atmospheric mass loss has significantly eroded their atmospheres. Here, I will delve into our work using the Transiting Exoplanet Survey Satellite (TESS) mission to detect, characterize, and study the population of short-period Neptunes around stars in nearby (< 200 pc) young clusters (< 1 Gyr) .This presentation will include the introduction of four new young planet candidates currently being validated through observational follow-up. Using our sample of detected planets and characterizations of our survey’s sensitivity, we measure an occurrence rate for young close-in Neptunes and sub-Neptunes. I find that the frequency of these young planets is a factor of 2-3x higher than their Gyr-old counterparts — much higher than previously predicted by planet formation and evolution models. This finding stands as one of the first demographic indicators that the radius distribution of small, short-period planets has evolved over time, likely influenced by atmospheric mass loss.