  Recent ALMA observations may indicate a surprising abundance of sub-Jovian
planets on very wide orbits in protoplanetary discs that are only a few million
years old. These planets are too young and distant to have been formed via the
Core Accretion (CA) scenario, and are much less massive than the gas clumps
born in the classical Gravitational Instability (GI) theory. It was recently
suggested that such planets may form by the partial destruction of GI
protoplanets: energy output due to the growth of a massive core may unbind all
or most of the surrounding pre-collapse protoplanet. Here we present the first
3D global disc simulations that simultaneously resolve grain dynamics in the
disc and within the protoplanet. We confirm that massive GI protoplanets may
self-destruct at arbitrarily large separations from the host star provided that
solid cores of mass around 10-20 Earth masses are able to grow inside them
during their pre-collapse phase. In addition, we find that the heating force
recently analysed by Masset and Velasco Romero (2017) perturbs these cores away
from the centre of their gaseous protoplanets. This leads to very complicated
dust dynamics in the protoplanet centre, potentially resulting in the formation
of multiple cores, planetary satellites, and other debris such as planetesimals
within the same protoplanet. A unique prediction of this planet formation
scenario is the presence of sub-Jovian planets at wide orbits in Class 0/I
protoplanetary discs.
