  Recent detailed observations of protoplanetary discs revealed a lot of
sub-structures which are mostly ring-like. One interpretation is that these
rings are caused by growing planets. These potential planets are not yet
opening very deep gaps in their discs. These planets instead form small gaps in
the discs to generate small pressure bumps exterior to their orbits that stop
the inflow of the largest dust particles. In the pebble accretion paradigm,
this planetary mass corresponds to the pebble isolation mass, where pebble
accretion stops and efficient gas accretion starts. We perform planet
population synthesis via pebble and gas accretion including type-I and type-II
migration. In the first stage of our simulations, we investigate the conditions
necessary for planets to reach the pebble isolation mass and compare their
position to the observed gaps. We find that in order to match the gap
structures 2000 M E in pebbles is needed, which would be only available for the
most metal rich stars. We then follow the evolution of these planets for a few
My to compare the resulting population with the observed exoplanet populations.
Planet formation in discs with these large amounts of pebbles result in mostly
forming gas giants and only very little super-Earths, contradicting
observations. This leads to the conclusions that either (i) the observed discs
are exceptions, (ii) not all gaps in observed discs are caused by planets or
(iii) that we miss some important ingredients in planet formation related to
gas accretion and/or planet migration.
