  The ubiquity of super-Earths poses a problem for planet formation theory to
explain how they avoided becoming gas giants. Rapid recycling of the envelope
gas of planets embedded in a protoplanetary disc has been proposed to delay the
cooling and following accretion of disc gas. We compare isothermal and
non-isothermal 3D hydrodynamical simulations of the gas flow past a planet to
investigate the influence on the feasibility of the recycling mechanism.
Radiative cooling is implemented by using the beta cooling model. We find that,
in either case, gas enters the Bondi sphere at high latitudes and leaves
through the midplane regions, or vice versa when disc gas rotates
sub-Keplerian. However, in contrast to the isothermal case where the recycling
flow reaches the deeper part of the envelope, the inflow is inhibited from
reaching the deep envelope in the non-isothermal case. Once the atmosphere
starts cooling, buoyant force prevents the high-entropy disc gas from intruding
the low-entropy atmosphere. We suggest that the buoyancy barrier isolates the
lower envelope from the recycling and allows further cooling, which may lead
runaway gas accretion onto the core.
