For 10 points, name these massive planets that have thick atmospheres, like Jupiter.
In one model for the formation of these things, they can only form when the Toomre Q parameter is less than one; their formation may also occur if they fall within a Stromgren sphere. In another model for the formation of these things, a transition to oligarchic growth occurs when the stirring ability of large bodies exceeds that of small bodies. That transition occurs sooner in high-metallicity environments since surface densities are enhanced. If one of these things suffers complete hydrodynamic escape, it is classified as Chthonian; COROT-7b may be one such body. In the Nice model, some of these things (*) migrated radially outwards after the Late Heavy Bombardment. These bodies may have a net outward heat flux arising solely from the Kelvin-Helmholtz mechanism. For 10 points, name these massive planets that have thick atmospheres, like Jupiter.
In one model for the formation of these things, they can only form when the Toomre Q parameter is less than one; their formation may also occur if they fall within a Stromgren sphere.
gas giants [prompt on "(giant) planets"]