Giant Planet Formation by Disk Instability

Two mechanisms have been suggested for forming giant planets, core accretion and disk instability. Each of these mechanisms has a long list of advantages and disadvantages. In order to further study the disk instability mechanism, 3D gravitational hydrodynamical models of protoplanetary disks have been constructed starting from realistic initial temperature and density profiles. The 3D models show that a clumpforming disk instability can occur in marginally unstable disks with masses as low as 0.04 M inside 10 AU, and perhaps even in somewhat lower disk masses, though a firm lower limit seems to be about 0.01M inside 10 AU. Models with doubled radial extent show that the outer boundary conditions do not unduly affect the results, and imply that clump formation may be limited to an annulus in orbital radius between about 5 AU and 12 AU. These models suggest that a protoplanetary disk with a mass at the high end of the range (0.01 to 0.07 M ) considered possible for the minimum mass solar nebula could quickly lead to the formation of two giant gaseous protoplanets, one at 6 AU and one at 12 AU. The terrestrial and outer planets could then form much later by the usual process of collisional accumulation.