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 disk dictates the outcome. The star
retains measures of the initial heavy-element (metal) abundance that can be
used to map solid masses onto 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.Comment: 5 pages, 2 figures; accepted by MNRA
