Predicting the frequencies of diverse exo-planetary systems

Abstract

Extrasolar planetary systems range from hot Jupiters out to icy comet belts more distant than Pluto. We explain this diversity in a model where the mass of solids in the primordial circumstellar disc dictates the outcome. The star retains measures of the initial heavy-element (metal) abundance that can be used to map solid masses on to outcomes, and the frequencies of all classes are correctly predicted. The differing dependences on metallicity for forming massive planets and low-mass cometary bodies are also explained. By extrapolation, around two-thirds of stars have enough solids to form Earth-like planets, and a high rate is supported by the first detections of low-mass exo-planets. © 2007 The Authors. Journal compilation © 2007 RAS.