planet demographics

Planet demographics, the occurrence rate of planets (especially including extra-solar planets) and occurrence rate of specific planet characteristics, grows in interest with the ongoing improvements in detecting and observing them, with thousands now known and a growing number with reasonable mass and radius estimates, and/or transmission spectrography data. Such demographic study is a work in progress: new data constantly becomes available, and the current data is incomplete due to specific gaps, two obvious ones being the smallest planets and the planets furthest from the host star. The field is new and researchers are producing varying numbers, but there is some consensus regarding some general characteristics. Individual studies often have caveats regarding the type of stars and planets: specifying particular planet radius and/or mass, planet orbital period, and/or spectral class of host star. Some generalities regarding typical main sequence stars (F-type through M-type stars which account for 99% of such stars):

• planets are common: the mean number of planets for such stars is at least one.
• smaller planets (rocky planets) are far more common than larger ones, occurring in the order of half of such stars.
• giant planets are rarer, occurring on the order of a tenth of such stars.
• super-Earths (somewhat larger than Earth) are the most common, with estimates as high as two thirds of such stars.
• both small and large planets occur more often around higher metallicity stars.