Exoplanets are revolutionizing planetary science by enabling statistical studies of a large number of planets. Empirical measurements of planet occurrence rates inform our understanding of the ubiquity and efficiency of planet formation, while the identification of sub-populations and trends in the distribution of observed exoplanet properties provides insights into the formation and evolution processes that are sculpting distant Solar Systems. In this paper, we review the current best estimates of planet populations. We focus in particular on η⊕, the occurrence rate of habitable zone rocky planets, since this factor strongly influences the design of future space based exoplanet direct detection missions.
Leslie A. Rogers, Leslie A. Rogers,
"Current best estimates of planet populations", Proc. SPIE 9836, Micro- and Nanotechnology Sensors, Systems, and Applications VIII, 983602 (17 May 2016); doi: 10.1117/12.2223920; https://doi.org/10.1117/12.2223920