Planetary Populations from Transit Surveys

Through decades of observations, astronomers have detected and confirmed nearly 4000 planets with orbits that cause them to pass in front of their host stars and cause periodic dimming events. These “transiting” planets are particularly valuable for follow-up studies because the time between consecutive dimming events reveals the orbital period and the amount of dimming reveals the size of the planet relative to the size of the host star. In addition, the atmospheric properties of transiting planets can be probed by comparing spectra obtained at different orbital phases. In this talk, I will briefly discuss the strengths and limitations of the transit method before reviewing our current understanding of the demographics of transiting planets. I will focus on planets smaller than Neptune because these worlds are particularly prevalent at the short orbital periods at which planets are most detectable via the transit method and because the size distribution of the smallest planets holds valuable clues about the processes governing atmospheric mass loss. While some transiting planets appear to be the only planet orbiting their host stars, transit surveys have revealed that systems of multiple planets are common and frequently contain tightly packed planets with small mutual inclinations. I will describe common trends observed for multiplanet system architectures and address how the number, size ratios, and period ratios of planets may provide hints about their formation and evolution. Finally, I will discuss correlations between host star properties and the characteristics of their accompanying planetary systems.