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There has been disagreement currently about whether cooling in protoplanetarydisks can be sufficiently fast to induce the formation of gas giantprotoplanets via gravitational instabilities. Simulations by our own group andothers indicate that this method of planet formation does not work for disksaround young, low- mass stars inside several tens of AU, while simulations byother groups show fragmentation into protoplanetary clumps in this region. Toallow direct comparison in hopes of isolating the cause of the differences, wehere present a high resolution three-dimensional hydrodynamics simulation of aprotoplanetary disk, where the disk model, initial perturbation, and simulationconditions are essentially identical to those used in a set of simulations byBoss. As in earlier papers by the same author, Boss (2007, hereafter B07)purports to show that cooling is fast enough to produce protoplanetary clumps.Here, we evolve the same B07 disk using an improved version of one of our ownradiative schemes and find that the disk does not fragment in our code butinstead quickly settles into a state with only low amplitude nonaxisymmetricstructure, which persists for at least several outer disk rotations. We see norapid radiative or convective cooling. We conclude that the differences inresults are due to different treatments of regions at and above the diskphotosphere, and we explain at least one way in which the scheme in B07 maylead to artificially fast cooling.

Giant Planet Formation by Disk Instability: A Comparison Simulation With An Improved Radiative Scheme