Planet populations as a function of stellar properties

Exoplanets around different types of stars provide a window into the diverse environments in which planets form. This chapter describes the observed relations between exoplanet populations and stellar properties and how they connect to planet formation in protoplanetary disks. Giant planets occur more frequently around more metal-rich and more massive stars. These findings support the core accretion theory of planet formation, in which the cores of giant planets form more rapidly in more metal-rich and more massive protoplanetary disks. Smaller planets, those with sizes roughly between Earth and Neptune, exhibit different scaling relations with stellar properties. These planets are found around stars with a wide range of metallicities and occur more frequently around lower-mass stars. This indicates that planet formation takes place in a wide range of environments, yet it is not clear why planets form more efficiently around low-mass stars. Going forward, exoplanet surveys targeting M dwarfs will characterize the exoplanet population around the lowest-mass stars. In combination with ongoing stellar characterization, this will help us understand the formation of planets in a large range of environments.