Stopping Super-Earths from growing into Jupiters

Super-Earths are by far the most dominant type of exoplanet, yet their formation is
still not well understood. In particular, planet formation models predict that many
of them should have accreted enough gas to become gas giants. Here we examine the
role of the protoplanetary disk in the cooling and contraction of the protoplanetary
envelope. In particular, we investigate the effects of 1) the thermal state of the disk as
set by the relative size of heating by accretion or irradiation, and whether its energy is
transported by radiation or convection, and 2) advection of entropy into the outer envelope by disk flows that penetrate the Hill sphere, as found in 3D global simulations.
We find that, at 0.1 AU, the envelope quickly becomes fully radiative, nearly isothermal, and thus cannot cool down, stalling gas accretion. This
effect is significantly more pronounced in convective disks, leading to envelope mass or-
ders of magnitude lower. Entropy advection at 0.1 AU in either radiative or convective
disks could therefore explain why super-Earths failed to undergo runaway accretion.

Ali-Dib, Cumming, & Lin (MNRAS 2020)