Tidal Downsizing model-IV. Destructive feedback in planets

The role of negative feedback from amassive solid core on its massive gas envelope in the TidalDownsizing scenario of planet formation is investigated via one-dimensional planet evolutionmodels followed by population synthesis calculations. It is shown that cores more massivethan ∼10M⊕ release enough energy to reverse contraction of their parent gas envelopes,culminating in their destruction. This process may help to explain why observed gas giantplanets are so rare, why massive cores are so ubiquitous, and why there is a sharp rollover inthe core mass function above ∼20M⊕. Additionally, the short time-scales with which thesemassive cores are assembled in TD may help explain formation route of Uranus, Neptune andthe suspected HL Tau planets. Given the negative role of cores in assembly of gas giants in themodel, an antimony is found between massive cores and gas giants: cores in survived gas giantplanets are on average less massive than cores free of massive envelopes. In rare circumstanceswhen core feedback self-regulates, extremely metal-rich gas giants, such as CoRoT-20b, a gasgiant made of heavy elements by up to ∼50 per cent, can be made.