Early planet formation as a trigger for further planet formation

Recent discoveries of extrasolar giant planets at small orbital radii(1,2), or having significant orbital eccentricities, suggest that the planets interacted with the disks of dust and gas from which they and the central stars formed(3-6). Here we show that if a gas-giant planet reaches a mass of 4-5 jovian masses sufficiently early, when the protoplanetary disk is still massive, an otherwise stable disk will fragment into additional planetary bodies. This process of catastrophic planet formation could account for the apparent difference(1) in the distribution of the masses of massive planets and brown dwarfs around other stars, and the existence of young stars that appear to have dissipated their disks at a very early age(7). Subsequent gravitational interactions(5,6,8,9) between the first planet to form and the additional planets could lead to planetary systems comprising a small number of massive planets in eccentric orbits.